Brushless Revo + A123 and ICE

[BrianG]

The Xtrema has a 180w limit. So, taking into account charger efficiency of about 75%, that is 240w. At 12v, that is 20A. Of course, if you aren't using the charger to it's max rating, it won't need that.

That 12v, 9A supply can put out 108w. Figuring charger efficiency, that supply can be used with a charger that will draw 81w. So:
At 3s, that is 6.43A max charge rate
At 4s, that is 4.82A max charge rate
At 5s, that is 3.86A max charge rate

This calculator can help pick a suitable supply. It really depends on what voltage and current you will be charging at and what the power limit for that specific charger.