NiMH batteries have become the mainstay in mobile consumer electronics. The main reasons for this are:

  • They have a large capacity -as much as 2000mAh in a single AA cell.
  • They are light-weight. Again, an AA cell weighs about 40grams.
  • They are easy and safe to handle. Although the different kinds of lithium based technologies offer a higher energy density,
    they have an annoying tendency to explode when mishandled(that's why Li-Ion batteries only come in intelligent packs that can take care of themselves).
  • It's Really Worth It(tm) to use NiMH batteries instead of alkaline -although you can get something like four or five alkalines for the price of one NiMH battery,
    you have something in the vicinity of 800 charge cycles in one NiMH.
  • Over the last five years or so, NiMH capacities have been steadily on the rise. 2000mAh for an AA cell is the current maximum -expect to see larger capacities in the future. To put this in the right context, alkaline batteries typically store 1500-3000mAh, but it's important to remember that rechargeables only drive 1.2 volts per cell where alkaline batteries are 1.5 and that means slightly less hours in a NiMH battery per charge.

    Now, before you go out on a NiMH shopping spree, there is an important issue with NiMH batteries. This particular gremlin is called internal resistance.
    All batteries have this. It's very low in NiCD and lead-acid batteries and notoriously high in NiMH and (in particular) lithium-technology cells.

    The effect of a high internal resistance is that as you draw more current from a battery, the voltage at the terminals drops quite a bit. This means that NiMH batteries should mainly be used in electronic equipment that draws relatively small currents over longer periods. It's not that a handful of NiMH cells can't drive something that depletes them in about ten minutes reasonably.
    The problem is that if you need a large current here and now (most likely for an electrical engine - and probably R/C uses), you just won't get it. This is of no concern to users who don't need large currents, but at least I've warned you now.