RE: How big of a generator do I need ?
My chargers (iCharger1010) have a storage (discharge) feature - it's incredibly slow, maybe 5-8hrs, to discharge a full pack to storage.
However, they do have 'regenerative discharge' - if hooked up to a battery instead of a power supply, they will discharge faster. Haven't tried it yet though, but plan on buying a small 12V tractor battery for discharging purposes to see.
Storage is about 3.8v/cell.