We have not charged 8 cell packs, but with the 7 cell IB3800 packs always stays at 5 amp both packs when charging, only if the electricity of the house is fluctuating it will drop to 4.5 amps.
I think the Super Brain 977 has a good power supply even though it`s rated at only 10 amps.

lawtyger, don`t worry about overcharging the batteries, each pack will stop when its fully charged no matter if the other is still charging.