Rechargeable Batteries

One of the best things I’ve ever bought in terms of photography equipment is my external flash unit – a Canon Speedlite 580EX. It makes such a huge difference to the quality of photographs, both indoors and outdoors. One of the best pro tips I’ve ever received is always use flash when shooting a wedding: it brings faces out of the shadows nicely, even on a sunny day.

The flash unit is significantly more powerful than the on-camera flash unit of my Canon 350D (GN 58 vs. GN 13), but this means it needs its own power supply. This is provided by an additional battery pack externally or 4 x AA batteries internally. Now alkalines last ages, but the environment thing is a consideration nowadays, and buying packs of Duracell AAs quickly gets expensive. So off I went and bought some Fameart 2700mAh AA rechargeable NiMH cells.

The initial test was good – fully charged in an hour and flash fires well: great. I put the camera kit away and then forgot about it. Next time I came to use it though, the batteries only lasted a couple of test shots. No problems – I thought there may be a few cycles needed before full capacity was reached. I put the alkalines back in and continued with the picture session. Same thing happened the next time, and I duly recharged them.

By the fifth time round though, I was beginning to get worried. The cells didn’t seem to be holding their charge at all. I was about to send an e-mail to the manufacturers, but then started Googling around looking for an answer, or reports of people hitting the same problem.

The main evidence came from the wonderfully-titled BatteryUniversity.com website. That gives a lot of information on battery characteristics, including these two very interesting facts:

  1. Self-discharge per month at room temperature is around 20% for NiCd cells and around 30% for NiMH cells
  2. The self-discharge is highest immediately after charge, and then tapers off. The capacity loss of NiCd is 10% in the first 24h, then declines to about 10% every 30 days thereafter. High temperature increases self-discharge.

Hmmm… assuming NiMH suffers like NiCd, 10% lost in the first 24 hours is a lot. The whole self-discharge theory was worth looking at though. I put the cells in a battery holder, then inside a sealed plastic bag, into the freezer. A month later, charge was still fine and happily powered my flash for a full session without having to resort to alkalines.

So when not in use, my batteries are now stored in the freezer – when I visit anyone for a weekend and ask to put the batteries in the fridge, I get some odd looks though!

The flip side is that batteries are much better at operating once they’ve gone above freezing, preferably into double-figures degrees-C. So I need to take batteries out of the freezer, then put them in my back trouser pocket while they warm up. Ah well, can’t have it both ways I guess…

From this blog entry you should take the following messages:

  • External flash is good
  • Buy rechargeable batteries
  • Store them in the freezer