Category Archives: Batteries

How to Not Lose (Much) Sleep

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Save the Wonder II [C_070237]

one hour payday loans

If you want to catch the good stuff… like a meteor shower, or the Milky Way rising in Spring you have to be up in the wee hours. After midnight up to perhaps sunrise.  There are some tricks to pulling this off without collapsing – or worse, falling asleep at the wheel.  One problem with doing night photography is that motels and hotels aren’t particularly suited to the night photographer who would prefer to get to bed after breakfast and sleep until dinner – you often end up paying for two days worth of room that you only use for 8 hours!

So here are some ways you can “Store up Sleep” to support your night habit.

The No Stay Method

  • Get plenty of sleep in the afternoon.
  • Drive from home to the event.
  • Do the shooting
  • Get Breakfast
  • Nap on a cot, pad or bench
  • Drive back home, stopping to rest or nap as needed.

Obviously you can try to get to the shooting location sooner, but for most people it’s not safe to not get proper rest especially if you’re driving.  For example, if I know I want to shoot a milky way rise – I work backward from my arrival time.  Let’s say I need to be on site at 3:00 am and it is a 5 hour drive. That means I will want to hit the road at 10:00 pm. It might sound scary to drive from 10 pm to 3 am, but if you’re properly rested you may find the lack of traffic refreshing and the travel time that much quicker – I do this all the time!  To pull this off, see my “Body Clock Reprogramming” method.

Stay and Play method

  • Arrive in the early afternoon.
  • Check in to an area hotel, motel or campsite.
  • Get lunch.
  • Retire EARLY for sleep.
  • Get up EARLY (depends how far away you are from the location) Perhaps a 2:30 AM or earlier.
  • Do the shooting.
  • Get Breakfast
  • Get back to the hotel in time for at least an hour or two (or ask for late checkout)
  • Check out and go home… or stay another night.

Body Clock Reprogramming

A lot of people claim that they can’t sleep during the day. Hogwash, I say.  If I know I’m going to do a long weekend of night shooting, I can push my body clock around a little – in spite of my day job. For example, if I know I’ll be shooting mostly in the pre-dawn hours, starting on Wednesday, I’ll go to bed an hour earlier and get up one or two hours earlier. If you don’t get out of bed until 9:00 am… you’ll have to start reprogramming on MONDAY.  Do this each day before the trip – go to bed an hour or two earlier and get up an hour or two earlier the following morning.  If you normally arise at 6:30 (like I do), after two days you will find you’re easily awake at 2:30 AM – perfect!  And a day later you won’t have much trouble getting up at midnight and plowing through perfectly perky until well after breakfast.   Just remember to avoid caffeine and stimulants!  By the way, altering your body clock like this is a great way to get ready for an upcoming trip to another time zone.

If you can’t push your body clock that far, then plan to sleep or nap at your shooting location. I usually bring a fully reclining chair, a comfortable pillow and TWO sleeping bags – one very warm one, one that is only meant to take the chill off. I can then either sleep out-of-doors, or if necessary in my car.  This works well if I’m running a timelapse or star trail – the intervalometer does all the work. In fact, while I was taking the shots for this timelapse/startrail:

The Cove [C_071837-940br]

I was a dozen feet from my camera in my car out of the wind checking the progress every once in a while on my CamRanger. I didn’t have to leave the car except to change batteries or memory cards!  I didn’t have to use the CamRanger, of course, an intervalometer is just fine. There is an advantage to using a Canon for unattended operation, however. That red “exposing light” on the back of the camera can be seen from a long way off. I can easily and quickly take a look and know that the camera is doing its thing. With the Nikon, you have to watch carefully for the “green flash” as it writes to the memory card – if you have 6 minute exposures, you may have to wait a LONG time.  The CamRanger makes it a bit easier because I can also check the images, and the camera battery status, and memory card status remotely.

Leave The Gear

Oh, and there is one more way: set your camera up, leave, and come back for it. I usually aim to return BEFORE dawn because few humans bother to be out before the sun is up. My gear has been left alone in the wild quite often.  Of course I’ve already triple checked and prepared for the weather conditions and I place my camera where it’s not easily located – except by me. It’s a good idea to triple check all your settings. More than once I’ve left and upon return found I forgot a setting. For a belt and suspenders approach, I also keep track of the camera’s exact location with a GPS or by “dropping a pin” on my iPhone. Of course the downside here is you may need a huge memory card, a super strong battery, and you can’t have too much separation anxiety about leaving your gear. It won’t do you any good if you leave and DON’T get any sleep because you fear for the safety of your gear.  Trust me, your gear is braver than you are!

Sometimes when we run workshops, we take turns guarding the gear for one another, so you can also agree to leave a guard soldier behind if you shoot with buddies.  Just be sure to be kind to your guard – they will likely be grumpy.

Untimely Battery Death: How to Avoid It.

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As a night photographer I’m a proponent of the philosophy of “carry a big battery” and you’ll never miss that shot.  However I learned a hard lesson about my corral of batteries that I feel I must pass on before you too shriek in terror when you find your once reliable battery has met an untimely (and inconveniently timed) demise.

Lithium Batteries are Greatly Disturbed By Heat

This was the lesson I learned the hard way. I had a stable of five fully charged batteries ranging in size from 1800 milliamp hours all the way up to 8,000 milliamp hours. I kept them in a shaded part of my car through some summer days in the San Francisco Bay area.  And that was how I learned that Lithium + Fully Charged + Heat = premature death.  The two low capacity batteries previously allowed me two and a half hours worth of continuous night exposure. Now they each last about 12 and 15 minutes.  The three HUGE batteries that could easily power my camera all night long for continuous exposures now have about the same life in them as my regular 2000 mA hr batteries – that is, about 1/3 as long as they used to last.

I learned why my brutish batteries became so feeble at Battery University.  In a nutshell I discovered that storing batteries cool (less the 86 F) and at 40% charge is the most effective at prolonging their life.  What I do now is keep all of my batteries in a separate pouch which I take with me into my office or home – even if I leave my camera equipment in the car.

I’d like to heed the 40% storage method – but not all of my chargers accurately tell the battery capacity. And worse, when I’m running out for a night of exposures, I usually don’t have an extra hour or two to fully charge my workhorses.

And yes, repeated discharge and recharge of those batteries will diminish their life, but NOT as fast as fully loaded batteries baking at a mild 90 degrees or more.

 

Astro101: Checklist

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From the simple to the extraordinarly complex here is a list of things to take when you venture out to do astrophotography:

Starter Kit – Camera & Tripod

  • Camera
  • Wide field, fast lens (40 degrees or more, f/1.8)
  • Sturdy Tripod
  • Intervalometer – though a simple remote push button will work, too.
  • Memory cards
  • Batteries (plenty)
  • Binoculars
  • Green Laser (optional), see Target that Fuzzy
  • Planisphere / star chart / smart app like Star Walk.
  • Red head lamp / flashlight with red cellophane over them.

That’s about it.  This approach allow visual observation, and photographs of large areas of e.g. the Milky Way.

Intermediate Kit

Starter kit plus:

  • Intervalometer
  • Equatorial Drive + Polar scope + batteries  (Polarie for example)
  • Head/mount to put the camera on the Equatorial drive.
  • Stadium cushion or garden kneeler
  • Telephoto lens (zoom or prime)
  • Bahtinov Mask (focus aid)

Serious Intermediate Kit

All of the above plus:

  • Deep cycle marine battery (or astro power kit)
  • Laptop with imaging aid program (e.g. BackyardEOS, MaximDL, …)
  • BIG battery for your camera (or converter to use astro power kit)
  • Voltage inverter to power the laptop
  • Red cellophane to cover the laptop screen
  • Small folding table
  • Folding chair
  • Power strip, extension cords
  • Power inverter (convert 12 VDC to AC)
  • Modest sized apochromatic refactor, mounting rings, extensions, eyepieces, star diagonal, dual speed focuser, dovetail plate, heads up finder.
  • Optional: GoTo solution for the mount

Sold Out Astroimager

  • Large APOchromatic refractor or Reflector
  • Massive mount with GoTo control
  • Astro CCD image camera with thermo electric cooling
  • Filters for Hydrogen Alpha, Oxygen, etc.
  • Finder scope
  • Guide scope and autoguider
  • Lots of $$$$.
  • Large car to drive it around.
  • (optional) Sherpa to lift it all.

For more information, please attend a Webinar!  See the training list here, or see all events here.

Collecting and Processing Images

I have a Canon, and an windows machine. These two things together mean that I can use BackyardEOS ($25) to aid in the focusing and capture of night sky images; and I can use Deep Sky Stacker (Free!) to process my images.  Deep Sky Stacker takes some patience to learn, but it is mostly automated.

I understand “Keith’s Image Stacker” ($15) is available for Mac people – though apparently it’s not quite as powerful or as widely used as DeepSkyStacker.

Pricier and more complete options include ImagePlus, MaximDL, and much more. For a full list of options, prices and features, please see Jerry Lodriguss’s site.

 

Power On – all Night Long!

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This is a revised article adapted from a tip featured on my prior (now defunct) website. Since I am a Canon owner the tips here are mostly specific to Canon, but there are some Nikon tips too.

Figure 1: Luggable (9,000 mAh, 10 pounds) Big.

I have built two different rigs for powering my Canon 40D, 50D and 5D Mark II cameras. Each of the beefy battery solutions here can run continuously for up to a dozen hours – and longer. When I say a dozen hours I mean a dozen hours of continuous shooting. One rig I call my luggable weighs about 10 pounds and uses a 12 volt, 9,000 mAh sealed lead acid battery in a box that can be used to jump start a car – it has jumper cables on it.  The total capacity of the battery is 108 watt-hours. My second lightweight solution is 7.4 volt, 8,000 mAh (56 watt-hour) combo that is much more portable because it weighs less than two pounds. I explain what “mAh” and “watt-hour” mean in the glossary below. To power a Canon DSLR a battery eliminator is required. Battery eliminators can be purchased from Canon ($$) or after market companies ($) or the can be fabricated (¢) by anyone who knows which end of a soldering iron is safest to hold. See below under “Battery Eliminator” for options.

*If you have a Nikon, e.g. model D200 you may find a somewhat simpler solution – or more complicated depending on your point of view. The D200, for example, can be paired with  the EH-6 AC adapter which mates with a DC power connector on the camera. The EH-6 apparently supplies 13.5 Volts to the connector. One D200 owner found that he could attach a 12V battery directly to the DC-in connector and power his camera. And attaching a 7.4V battery seemed to work just fine! Unfortunately the on-camera connector is not a standard size so it seems nearly impossible to get one without plunking down cash.

Figure 2: Lightweight, Small, Powerful (8,000 mAh, 1.3 pounds)

So why did I bother to build these things? I typically like to hike into the wilderness, set up my rig for star trail work and go to sleep. The shutter will be open nearly continuously for 4, 6 or even 8 hours at a time. While my descriptions are specific to the Canon, a similar approach works for other cameras and camera vendors. Indeed, the Nikon D40 battery, the EN-EL9, is a 7.4V battery, too.

Six hours of run time is more than can be achieved with a single high capacity battery and  also beyond the capacity of a battery grip that holds two high capacity batteries. Since I hike with my solution it must be portable.

The luggable rig pictured above in Figure 1 is obviously not ideal for hiking. The “Start It” unit weighs almost 10 pounds. On the other hand, I can keep the jump start kit in my car and perhaps avoid a dead car battery. The “Start It” will fully charge if I connect it to the car accessory power plug for 2-3 hours which is convenient when driving to remote locations.

The lightweight rig at about half the capacity is highly portable. Indeed, two BP-970 camcorder batteries totaling about 3 pounds exceeds the power of the luggable solution. Nontheless I use both solutions.

Let me walk through each solution.

Luggable Jump Start or Car Battery Based Solution

The Jump Start battery solution is good for more than just powering the camera. The heft of the battery makes it a pretty good ballast for stabilizing my tripod. The 12 Volt starter battery is also better suited for use with a dew heater to keep the camera lens from fogging, it can be used with other 12V appliances – anything that plugs into a standard car power socket (aka a cigarette lighter).  Sealed lead acid batteries can supply more power in very cold weather (freezing and below) than lithium technology. Oh, and you can use it to jump start your car if needed! The down side, of course, is it’s heavy. Not something you want to hike with for miles and miles (though I have). Also any power solution for based on a jump start battery can also work if plugged directly into a car! Here’s what you need:

  1. Portable power source one of
    • 12V Car battery or jump start device.
    • Your car (that power/cigarette lighter socket can come in handy)!
  2. DC-DC converter because a 12 volt battery is too strong to power a camera which wants to be fed 8.2 volts or less.
  3. Dummy Battery or Battery Eliminator options are:
    • Buy a battery eliminator: eg. the Canon DR-400 $30.
    • Cannibalize an old/non-working battery or hack up a new, cheap one.
    • Build a battery dummy out of wood, plastic, or similar non-conducting substance.
  4. Cabling and strapping to carry and secure the rig (I use a bungee cord to attach it to my tripod)

The device I bought, the Jump Start, is a small 12V auto battery with a carry handle, jumpers and a power port (cigarette lighter) socket.

The luggable solution also requires a DC to DC converter. The converter will accept anywhere from 12 to 18 volts and has a dial to select the output voltage with choices of 3/5/7.5/8/9 or 12 Volts. The $19 device lists itself as a 3000mA (3.0 amp) unit.  The converter has an inline fuse to “blow” if too much electricity runs through it – this is a good thing as it will help protect the camera and the battery. The device I purchased from Fry’s Electronic is labeled “3000 mA Rhino Intelligent Adapter” but I haven’t been able to match that with anything on the internet or find anything similar.  The closest match I found is a 1 Amp unit, or this unit.  Many people like me have a big assortment of “cigarette lighter” chargers, and one of them may be able to do the job. Inspect the unit carefully to determine its output voltage and capacity which are often labeled right on the unit. For example the label might read: Input 12VDC, Output: 7.5VDC 500ma which means its output is the right voltage, but at only 500 milliamps it may be too puny to keep the camera fed.

Figure 3: A 3amp 12V selectable converter which includes 7.5 V.

I discovered that an old Nokia cell phone charger, the Nokia LCH-8 converts 12 to 24V from your car battery to 7.5 volts DC at 650 ma. In theory this might be enough except that I’ve read reports on the internet that measured peak usage for the Canon is 1.4 amps (1400mA). Clearly the Nokia can’t sustain that much current, but if it is for a short period there is an electrical trick to allow this – add a big capacitor. I haven’t tried using the Nokia charger.

Other Luggable Soltions

There are other options, too. For example Harold Davis purchased the Vagabond II Portable Power System ($299). This is also a beefy (really beefy) battery which features 12 volt output and a built in inverter for powering a 120 Volt outlet. The battery sports 240 watt-hours. That is huge. The most serious detraction is the weight and bulk. It is a self contained system that weights 18.6 pounds. If the 120 volt output is used, it also means that an A/C adapter for the camera must be used. The Vagabond’s built-in inverter must be paired with an A/C adapter for AC-DC conversion. Converting power from 12 volts DC to 120 Volts AC and then back to a DC voltage will cause as much as 35% of the electrical energy to be wasted – but given the huge size of the battery and the additional versatility the loss of power may not matter.  A smaller, lighter cousin is also available the Vagabond Mini.  At $240 and 3.5 pounds total weight it is more portable. The unit still has a substantial 130 Watt-hour rating.

Lightweight Camcorder Battery Solution

The camcorder or Remote Control (RC) battery is a lighter and more portable solution that uses off-the shelf parts – but assembly is still required. Lithium technology does not supply as much power in very cold climates as a lead-acid car battery solution. Camcorder batteries are large compared to the 3oz battery for my cameras and camcorder batteries are relatively hefty at almost 1 pound. But, with that weight you get 5 to 7 times as much power! Taking two of these with you on a back pack trip is feasible. Not something you can say about a 10 pound solution! In fact, 8 pounds of Lithium Ion (camcorder  batteries) will last longer than 40 pounds of sealed lead-acid batteries.

At its core my lightweight solution is a camcorder battery and a charger suitable for that battery. I blatantly ignored the “do not disassemble” label on my charger. The unit I purchased has two  phillips screws located beneath a large sticker on the back. After disassembly I discovered that there was plenty of room inside the case for an additional power jack (6). I wired a power jack into the unit by finding where the spring loaded battery contacts went, carefully cutting the wires and attaching them to the power connector, then attaching wires from the power connector to the place the battery contact wires originally went. The power jack that I  added has a “Normally Closed” switch which completes a circuit when there is no plug in the jack. It was probably not necessary to take the precaution, but safety when 120 volts are involved is a good thing.

Figure 4: The components

I purchased these:

  • A: a replacement BP-970 Camcorder battery. Several capacities are available. I chose two 8,000 mAh batteries at $31 each from Amazon. I also purchased a charger for this battery.
  • B: a camcorder battery charger for the above battery.
    This @ $10, or this @$15 seems just fine. I have also purchased another charger: the Lenmar which is a tinkerers dream because it comes with easily modifiable plates to accommodate different batteries.
  • (1) 20 or 22 gauge stranded wire. I suggest red and black, but black wasn’t available so I used white. About $6
  • (2) M size inline power jack. $4 #274-1577
  • (3) M size power connector plug (two needed) $1.50 each  #274-1569
  • (4) electrical tape for strain relief $2
  • (5) 3/32″ heat shrink tubing $3
  • (6) M size chassis mount power jack.$3.50  #274-1582

I made these

  • B: charger with additional “battery out” power jack (6).
  • C: power cable using stranded 20 or 22 gage wire (1) with 3/32″ heat shrink tubing (5) at the ends and in the middle for strain relief and a (2)
    power jack. I also used a velcro cable tie for neatness (Home Depot?)
  • D: BP-511 battery eliminator – I gutted an old BP-511A battery unsoldering the circuit board with a low wattage iron. I then soldered a  length of red wire to the “+” lead and length of white wire to the “-” lead. I tied a loose knot on the inside (strain relief) and passed the ends through the battery case by making a hole with my soldering iron. I used the barrel of a recently turned off soldering iron to shrink the tubing until it was tight and made sure that where the wire entered and exited the battery it did so through the heat-shrink tubing. I the glued the
    battery case back together with hot melt glue along the corners on the inside.
  • E: Power connector (used M size power connector (2))
  • F: “Cheater” power cable – basically a length of double wires with a part number (3) soldered at each end.
    *** You may be wondering why I didn’t just put a plug  (3) at the end of the battery eliminator – it’s because a DC-DC converter will normally provide a PLUG not a socket. I can also make a longer or shorter cheater cord if need be.

The two screws that hold this unit together are underneath the big sticker on the back. I poked holes through the sticker using a phillips screw driver.

If you are uncomfortable with messing with the guts of the charger, you can modify a plate from the Lenmar charger instead. The Lenmar comes with interchangeable plates to accommodate different batteries. or you can get a cheap travel charger. I find it convenient that my charger and “battery connector” are the same unit. And the charger is quite light.

Not shown, but also required:

  1. low wattage soldering iron.
  2. Small gauge wire stripper.
  3. Diagonal cutter or needle nose pliers with cutter,
  4. small parts holder (chip clips will work).
  5. A drill (and drill bit of the appropriate size for the chassis mount jack (6)).
  6. You may also need a phillips, hex or regular screwdriver to disassemble the battery charger.I originally purchased a sub-mini audio connector and tried to use that as the power connector but the connection was not crisp or reliable.
  7. And finally you may also need contact cement and/or a hot glue gun to reassemble the battery eliminator and possibly the charger as well.
  8. Patience.

The Battery Eliminator

Unless your camera or battery grip has a power connector any “big battery”solution will require a battery eliminator (parts C, D and E) or a DC input plug (hooray to Nikon for getting this part right, boo for the lack of availability of those connectors!). You can buy a battery eliminator – see more below – for many cameras but I found it easy to make a battery eliminator for my BP-511 battery out of a junk battery. For Canon cameras the battery eliminator plugs in where the battery goes and wires exit through a rubber gasket and are then connected to an external power source. While making a BP-511 eliminator was easy, I also tried to make an LP-E6 battery eliminator from a new (but cheap) LP-E6. I gutted the battery and soldered wires. The outcome was less than stellar as the contacts in the LP-E6 are small and very close together.

Those who fear the soldering iron can purchase an ACK-E2 or a cheaper knock off. Had I found the $20 knock off I would not have bothered hacking up a battery.  The ACK-E2 includes a battery eliminator and an AC power adapter to power the camera from a 110 volt outlet – I almost never am near wall power, but I can use the battery eliminator.   For my other camera, the 5D Mk II Canon sells the ACK-E6AC. Cost is  about $140. Like the ACK-E2 the ACK-E6AC includes a battery eliminator and an AC wall unit. However I found an equivalent unit for $39. No need to struggle with disassembling and soldering a battery eliminator!

My two cautions about these knock off units are:

  1. I doubt the AC components are UL listed. The knock offs certainly feel cheap.
  2. The connector between the AC unit and the dummy battery is not standard. Different manufacturers use different connectors. The connector on my ACK-E6AC knock off matched the Radio Shack M size power plug I had already been using. Oh happy day!

NOTE: Some camera models, like the Canon 5D Mk II have batteries with “chips” in them to help the camera know the current battery state. Your camera may – or may not – require this chip. Without the chip the camera nags you whether it is “ok” to use a battery that it can not talk to.  Just say yes.

Figure 5: The homemade BP-511 battery eliminator installed in a Canon 40D camera.

Canon cameras have a little rubber gasket that allows a cable to exit the battery compartment. If you build your own eliminator make sure your cable exits your battery eliminator where it will be able to be routed out of the battery compartment. If you do it wrong, you’ll have a battery eliminator that does not work because most cameras do not supply power to the camera electronics unless the battery door cover is fully closed. This is also true for most battery grip attachments.

Voltage, Amperes and Stuff: Background Data for the Electronically Challenged

The typical Canon BP 511 battery supplies 7.4 volts** to the camera and boasts a 1390 milliamp-hour rating. 1390 maH means that if the camera draws 1.39 amps it could run for an hour. That kind of power is possible with lithium batteries – the most power for the least weight of any currently available options. It’s also possible with SLA (Sealed Lead Acid) and a variety of similar battery chemistries. The battery you have in your car is a suitable choice, it’s just quite a bit heavier than most people are willing to carry. Smaller lighter versions of that same battery are available for things like lawn tractors and, “Jump Starters”.

**First you need to know a little secret.
A “12 volt” battery is really around 13.8 volts when fully charged. Likewise the Canon 7.4V battery is about 8.2V when fully charged. During use the voltage will drop to the point where it will no longer be able to service the camera. At that point it is wise to stop using the battery… going further, especially with a lead acid type battery, may permanently damage the battery.

Using a 12 volt car battery with a camera that expects 7.4 volts is, well, a possible cause for problems. The camera probably CAN sip from the 12 volt supply, but it would be kindler and gentler to chop that voltage down using a “voltage regulator”. In particular a “DC to DC” regulator is best here. A DC to DC converter (sometimes called a “buck”) drops the voltage down to a manageable level.

Confused about Volts, Amps, MilliAmps?

Voltage = “pressure”. Imagine a ball. It’s useless unless filled – to the proper pressure with air. Fill it too much and it will pop, too little and it won’t bounce. The
electrical equivalent of “air pressure” is “voltage”. Just as car tires require more air pressure to work than soccer balls do, so do some circuits require more voltage than others.

Amps (or milliamps) = “flow rate”. It will take a lot less time for a tire to go flat if there is a huge hole where lots of air can escape than it will for a pin-prick sized hole. The “rate of escape of air” is the electrical analog of current which is measured in  amps. A milliamp is a thousandth of an amp.

Resistance. In our analog, the “size of the hole” is a good example of the electrical term resistance. And it’s not a surprise since the volume of air that can escape in a second will depend on the pressure and the size of the hole the air can pass through.

Capacitance. A capacitor is a device that can hold a charge. In the air pressure world, a tire is a capacitor. You can fill a tire with air, then use the pressure in the tire a little at a time – or all at once – to inflate something else like a balloon.

mAh – an abbreviation for milliamp-hour.

Milliamp-Hour is one milliamp of current for one hour.  Milliamp-hours or amp-hours describe how much energy a battery can supply and for how long – under normal conditions, that is.

Watt-Hour is another format for specifying the capacity of a battery. To convert from Watt-Hours to Milliamp-hours divide the Watt-hours by the working voltage and then multiply by 1,000.  Thus a 34.2 watt-hour (wH) 7.2 Volt battery has a 4,750 mAh capacity. To convert from amp-hours to watt-hours multiply the amp-hours by the working voltage. If starting with milliamp-hours first  divide by 1,000. A 7.4 volt battery with 7,000 mAh rating is equal to 7,000 / 1000 * 7.4 which is 51.8 Watt-hours

Here is another important tidbit… just because a charger for a camera battery is available does not mean the charger can be used in place of the battery. There are two reasons for this.  The first reason is that chargers MUST supply more than the normal maximum battery voltage. Using an air-pressure analogy: to fill a tire, the pump must exert greater air pressure than the current pressure in the tire. Likewise to charge a battery, a greater voltage must be applied than the final voltage the battery will attain. The second reason is that the charger does not have to supply much current, a trickle is all it needs to slowly charge the battery – just as a bicycle pump can inflate a truck tire. The camera, however, sometimes takes “gulps” of current – more than the charger may be able to supply.

Knowing that a 7.4V battery is really about 8.2V helps makes it clear that ANY voltage in the range of about 7 to 8.5 volts will make a (Canon) camera happy IF it can also supply enough amps.

Discussions

Timescapes.org has a lot of great discussions.