charger help - what charge rate

[BrianG]

You mean how many amps for the PS input into the charger? If it's the Duo 3+, the max input is 40A @ 12v.

That charger (if its the duo3+) is rated 350w X 2 only when hooked to a ~24v supply. At 12v, you are limited to 40A max, which is 480w max. That will be split between the two charger channels (when charging two packs at once). Minus efficiency losses, yadda yadda, you are left with around 220w x 2 channels. What current you can charge at depends on the voltage of the pack.