NiMH features:

No memory effect ! - NiMH's do not develop a 'memory' like NiCad rechargeable batteries. The memory effect is when a rechargeable battery is recharged before its power is fully depleated. Over time, the battery will suddenly require charging much sooner than before. An example of this can be seen with cordless phones. If you always put it back in the cradle after a short time of use, it will not last for long periods of time even though it seems to be fully charged !

Recharge 500-1,000 times ! - NiCad batteries seem to stop holding a charge after a while. They just don't last too long. Alkaline batteries must be thrown away or hopefully recycled when depleated. But NiMH's can be recharged many, many times. From 500 to 1,000 times under optimal conditions !

Inexpensive ! - NiMH's are inexpensive, about $2.50 for a AAA cell. This becomes very inexpensive when you factor in how many times you can recharge the battery. It's like getting 1,000 alkaline batteries for $2.50 !

Available in standard cells ! - NiMH batteries became popular with laptops and digital cameras. But you won't see standard cells (AA, AAA, C) in the super market or drug store. This is because the big battery companies don't want you to stop buying their disposable batteries. Their existance has been pretty well 'hushed up' in the US. Even products that are sold with NiMH batteries mislead us into beleiving that the battery life is more because of their products advanced circuitry rather than the batteries themselves ! But standard cells are produced in other contries (mostly Japan) and imported to the US !

Where to get yours ! - I have tested the NEXcell batteries and the MAHA MH-C204F 'Smart' charger from Thomas Distributing. I like the GP batteries better...they just seem to last longer for me. Thomas Distributing has AAA cells for your PalmPilot as well as the special chargers needed. A NiCad charger will not work. You must get a NiMH charger which runs about $27. Check out their website www.batterysupply.com for pricing, item numbers, online ordering, etc.
Radio Shack also sells the batteries and a charger but their prices are not as low as online vendors.

Tips for using NiMH's:

I am not an expert, but I have been using the NiMH's in my Pilots for a while now. Here are some tips that I can offer:
Buy two sets of NiMH's - (ie 4 AAA cells) so that you can have one set in use and one set ready to go!

Form pairs and keep them together - It seems to work best to pair off the NiMH's when you first get them, and then don't mix them up. When you first get them, test their strength with a battery tester before charging them. Group cells that have about the same amount of power before the first charge. Label them with a marker to keep the sets together. Appearantly, if one NiMH is stronger than the other, they sort of trade power when using or charging them, which can decrease their useful life.

Keep in mind - The AAA NiMH batteries are rated at 1.2 volts while Alkalines are rated at 1.5. Don't worry, the Pilot works with voltage all the way down to 2.0 volts so a fully-charged pair of NiMH's will run the Pilot for quite a while, but you will never see the battery gauge at 100% (3.0 volts).
Warning: Becareful not to let the NiMH's run down too low. The NiMH batteries seem to give out very quickly when they get down to about 2.3 volts on the Pilot, sometimes before the warning dialog box appears ! Replace them we the voltage gets down to the 2.3 - 2.4 range.