Photo Talk

I have written for club magazines over a long period. I'm helping with a magazine now, and will post the articles.

The care and feeding of Nickel Metal-Hydride Batteries

When you buy a digital camera that is suppled with alkaline batteries, you’ll find they last no time at all. Fortunately, help is at hand for these—and other high drain accessories like flash guns.

The Nickel Metal-hydride rechargeable battery (NiMH for short) replaces the earlier Nickel Cadmium rechargeables (NiCad) and are available in AA and AAA sizes. They have a 30% greater power capacity than an equivalent NiCad and are less prone to ‘memory’. This is an apparent decrease in capacity, which is usually reversed by a complete discharge followed by a full charge.

All batteries suffer a decrease in power over time due to self-discharge. NiCads will lose 20% of their charge in a month; NiMH will lose 30%. In other words, even if your batteries are unused, you still need to charge them before the next use.

This discharge rate is at room temperature; if you put fully-charged NiMH batteries in a deep freeze, they will retain 90% of their charge for several months. If you do this, put them in tightly sealed double bags to keep them dry. And let them return to room temperature before using them!

It is essential to use the correct charger for the battery type. When buying NiMH batteries, it pays to get the same manufacturer’s charger -- this will charge at the correct rate, and stop the charge when done. These batteries do not like being overcharged, so remember to remove them from the charger, as there is generally a small trickle charge going after the light goes out.

NiCad batteries will recharge about 1000 times; NiMH should go to 500 recharges if you have charged them carefully in the correct charger. They will lose a little capacity anyway, but this should be no more than 15% reduction.

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