Tuesday, September 17, 2013

The great mystery of NiMH high-capacity vs. low self-discharge, answered

NiMH batteries are cool, but they are expensive.  If you really want to "go green"* and switch wholesale to NiMH, it's a significant investment and you want to get the best stuff you can afford.

I know a lot of people out there don't know if they should go for "high-capacity" NiMH or "low-discharge" NiMH. I know it caused me a lot of consternation when I needed to replace my older cells - none of which were low-discharge type, so I had no experience to go by.

Here's my take: Low-discharge, hands down.

This is based on my experience - no formal tests, but the experience is so compelling I don't think it's even worthwhile testing.

Many of my NiMH batteries go into my SLR flash.  Obviously I do not use my camera every day, and it sometimes sits for weeks.  I also obviously want to be able to pick it up at any time and go to it, which I often do for work purposes.

Before, every third time I picked up the camera the flash batteries were weak.  This was with "high-capacity" NiMH cells.  It got so I had to put alkalines in to ensure the camera would be available when I needed it.

When I switched to Eneloops, this problem has all but disappeared.  I don't have to put alkalines into my flash anymore, as the Eneloops retain their charge in storage.

Sure, I might get a few less flashes out of the Eneloops overall in a straight, no-storage back-to-back test  But the usable capacity of the Eneloops far exceeds the other NiMH batteries I have around.

Now, in my electronic door locks, I haven't noticed much difference.  But I expect the Eneloops to last the same or longer, owing to their stability.  The regular NiMH seemed to work pretty well, though, so less of a difference there.  YMMV.

So, if you're one of those rare people that use batteries all day every day to exhaustion, get high-capacity.**  Everyone else should get Eneloops or similar low-discharge cells.  Even with the 10% capacity hit, you will get much more utility of out of them, no question.

Not to mention that you can charge them and store them out of the charger, which frees up your expensive chargers to do other things - like keeping those high-capacity cells you still have topped up and fresh.
I picked up a bunch of Eneloops from Amazon on a USA trip.  Twice, actually - the first ones worked out so well I needed more, about a hundred in total.  They're that good.  If you have the chance to buy them at a good price, don't hesitate, just do it.

I think they were around $2.50 each, which is break even in 5-6 uses.  The AAAs work well too.  Skip through Amazon to find the best prices, which will be on packs of about 8 cells. 

The "packages" of 20-100 cells were actually more expensive per cell, and not just because they were bundled with a charger.  If you need a charger, some big packages might be worth it, but otherwise go for the lowest per-cell cost you can find.  In my case this was from Amazon itself - not a third-party vendor - with free shipping (over $50).

(*  Whether NiMH cells are really more "green" overall is a debate I'm not getting in to.)

(** Besides which, if you're chewing 1-3 sets of NiMH cells a day, shouldn't you be using a big external pack or something?)