Hi Bryan,

You want to charge at a lower rate, 1.5 amps for a longer period, most digital chargers are peak chargers and will turn off when finished. I charge my hump packs and holders like you want to do at 1 amp. You will heat up the packs way to fast at anything above 1/5 amps.

I have the brain from mrc and i can set the amps, amount of batteries, etc. Our himoto charger (thats still in customs) have all these adjustments too.

Yes you can charge them in a 4 pack holder.