NiMh AA batteries

David Burren
November 2006

AA batteries are a familar tool to most photographers. On-camera flashes use them (either 4 or 5 at a time). Some compact cameras (and the Fuji S2 & S3 Pro DSLRs) use them. The Canon CP-E3 external flash power pack uses 8 of them. In my own kit my GPS also uses them, along with our 2-way radios (which use 3 each).

With all these batteries, rechargeables are great and the NiMH (Nickel Metal-Hydride) ones have become the defacto standard. They can supply relatively high currents (especially compared to the alkaline cells) and are less susceptible to charging issues than NiCd cells are. Mind you, they're not perfect for all applications. They self-discharge: their stored charge dissipates when they're not being used (typically 2-10% per day, depending on temperature). So putting NiMH batteries in a torch that spends most of its time on a shelf or in a camera bag waiting to be used, would not be a good idea. It would probably be flat when you needed it! The Li-Ion (Lithium Ion) batteries common in most digital cameras (and mobile phones) today do not suffer from self-discharge, but they're not available in AA size.

With all these devices using AA batteries, photographers often build up fairly large collections of batteries. How much power each battery holds is the basic feature that's important (note that as the batteries get older their capacity will reduce: eventually justifying replacing them, or at least only using them in less-demanding devices).

Chargers

The way you recharge the batteries can have a large effect on their capacity and longevity. Obviously undercharging a battery will limit the amount of power available, but overcharging will do the same on a more-permanent basis. Charging a battery too fast can also damage it. For this reason most chargers have basic overcharge protection built-in, and limit the charge current. However many chargers do this very poorly, and it's important to choose a good charger. Probably the most important feature to look for is to have individual charge circuits for each battery (typically with separate indicators: e.g. LEDs).

Cheap chargers offer the ability to charge only 2 or 4 batteries at a time. Unfortunately this assumes that all the batteries in the set are behaving identically. This is never true (especially as the batteries age) and the result is at least one battery ends up being overcharged, and the others are often under-charged. When one battery fails, the whole set fails (and can in fact be damaged by the charger). I recommend that you do NOT use a charger like this!

At the moment I have two favourite chargers:

There are many other chargers out there that will meet my basic feature recommendations, but these two are ones I personally like. They both handle AAA as well as AA batteries, although the only place I currently use AAA NiMH batteries is in the cordless phones in my house (they charge their own batteries) so this hasn't been important to me.

Some chargers will handle up to 8 batteries at once, and these may be useful if you have lots of batteries to recharge. However even when travelling with all my gear, I have been able to recharge all my batteries using just the BC-900. Having a larger charger might have been useful, but it will take up more space in your luggage, which can be very important (especially if travelling by air).

Choosing batteries

There are good batteries, and there are terrible ones. There are expensive batteries, and cheap ones. How can you distinguish them?

It's not easy, as the only pieces of information published about each battery type are the brand and the "capacity" (measured in milliamps/hour: mAh). In fact some manufacturers specify the average capacity, some the minimum or maximum, and some just give the batteries names that imply a capacity.

I have built up a small collection of batteries over the years, and using my La Crosse BC-900 charger in mid-late 2006 I have been able to measure the capacity of all of them. I have also gathered the results of the same testing from a friend in Sydney. You may be interested in the results:

The performance of all these batteries will degrade as they age, but this might give you at least a sense of their behaviour. A few brands are atrocious, many are reasonable, and some are excellent. Using good chargers is important in order to maximise the capacity and life of the batteries.

As you might guess, I quite like the PowerEx and PowerTech batteries.

Storing batteries

Carrying spare batteries, it's important to avoid accidental short-circuits as well as to keep each group of batteries together. When swapping the batteries in a flash unit, being able to pick out the batteries as a group without having to dig around in a bag or pocket is important, as well as having somewhere to put the spent batteries taken out of the unit. Especially as Professor Murphy will do his best to make sure that you're in a hurry whenever you need to swap the batteries!

I bundle each group of batteries together, and try to have a system where I can keep track of which group is charged and which is flat (by keeping them in separate compartments of my bags). I don't need to keep them in separate pockets of my photo vest, as I usually only have to carry a single spare group when I'm away from my camera bag.

PowerEx 4-cell carrier

Some photographers bundle groups of batteries together with elastic bands, but I have found two solutions that work well for me:

• Snap-lock bags
  These bags offer waterproof storage for groups of batteries, are available at almost any supermarket, and place no restrictions on the number of batteries in a group (useful if you use 5 batteries at a time in a Nikon SB-800 flash). They last quite a while before wearing out.
  The type I use is the GLAD Snaplock "MINI" (15x9 cm) size.
• Battery carriers
  Available to take 4 or 8 batteries at a time, these hard-plastic cases are compact and convenient. I've seen two types: PowerEx-branded ones from Maha, and no-name ones on eBay. I have examples of each, and I must say I prefer the PowerEx ones. They're only AU$3 each for the 4-cell versions. The 8-cell version is AU$4 (I use one of these to keep the spare batteries for my CP-E3 together).

Places to purchase these products

If you are in Australia and are interested in Maha or PowerEx products, I recommend talking to the Australian distributor: Servaas Products in Vermont (Victoria). If you're in the USA, I have in the past had good dealings with Thomas Distributing.

-- David Burren
November 2006