Useful technical pages I have found on the internet

All about batteries and cells, of several different chemistries (but especially NiCd), discharge cycles, dendrites, and cell life

A good battery SOC (state of charge) table for lead-acid batteries

Good technical information on charging lead-acid batteries

A battery SOC (state of charge) table for various chemistries (for large batteries, like automotive and marine)

Why Kill-A-Watt units die, "capacitive dropper" power supplies, and how to repair them