There are two types of NiMH batteries available: low self-discharge (LSD) and high self-discharge (HSD).
- Have a shelf life measured in months
- Usually marketed as "pre-charged" or "ready-to-use"
- Have a lower capacity range (2000-2400 mAh)
- Can be damaged if charged too quickly (faster than 60 mins is not recommended)
- Best for LB use: Maha Imedion 2400 mAh
- Have a shelf life measured in days, or weeks at best
- Have a higher capacity range (up to 2800 mAh)
- Can be used in fast chargers (15 mins)
- Best for heavy/frequent use: Maha Powerex 2700 mAh
Choosing between them depends on your usage habits. HSD batteries will only provide about 30% longer in use time (say, six solid minutes of "burn" time) which might or might not be significant. They need to be "topped off" every three days or so, but have the advantage that they can be put in a 15 minute charger.
LSD batteries, on the other hand, will remain "ready for use" once they are fully charged for months at a time -- people do not have to remember to put them back in the charger as frequently, or keep them there, to be usable. Unfortunately, LSD batteries do not handle 15 minute chargers as well -- they need a slower, more accurate charger.
If you mix the two types and also have a fast charger, be sure to mark them so that you don't put LSD batteries through a fast charge cycle. Doing this won't destroy them but it will reduce their lifetime much more quickly.