The robot (R2-D2) that I am building requires a MASSIVE battery. 800 Wh, to be precise. Cost is the primary driver, second to weight and volume. This, in combination to the high cost of any (non-lead) pre-made battery of this capacity has driven me to consider the design of a homemade pack of individual AA cells. The configuration in mind calls for the use of 240 (1.2-volt, 2.8-Ah) in a 10S-24P arrangement (12-volt, 67.2-Ah). This battery may commonly be drained to (or close to) zero. This inquiry has 3 parts.
BALANCING. I understand that normal Ni-MH packs (4.8, 7.2, 9.6, 19.2) do not require balancing. They need only be attached in series. However, I should consider this FAR from normal. Over the entire lifetime of this droid (~2 years), would a balancing circuit be ideal? If so, what suppliers exist for a single board capable of a 12-volt, 40-amp (peak) current?
CHARGING. A number of functionalities in droid require continuous operation, and must remain powered during charging of the battery. In addition, this droid will be used on a daily basis, and must be fully re-charged within 8 hours. Do any specific regulator circuits exist, capable of providing these characteristics for a Ni-MH pack of such size? Is a special converter of regulator required to prevent over-charging?
SAFETY. If additional equipment is not required for balancing, charging, or regulation, what are good practices? What is better for protection from overheating, short-circuit, and over-current draw (fuses, limiters, regulators, etc.)?