Give up on that memory thing, its a hold over from the Sixties when NASA was doing very precise charge and discharging of batteries to the same point. Not a problem these days. Nicads are generally still considered the most reliable battery out there and will take more abuse and have a lower internal resistance. Not to say that the other options won't work just fine. The downside to Nicads is weight and they are more toxic. I just don't see a need to spend money untill you really need to, If you need to, thats great, but lets see if you need to first.