I had a few of those similar B3 chargers that came with my ZD Racing ZRT-1 RTR truggies. It will take hours to charge even a 2S LiPo pack, and if you are using one charger to charge two 2S packs to run in a 1/8 scale platform...half your day is spent waiting for one run.
When I got my truggies, I had other chargers at the time, but was curious as to what power output the included chargers had. Mine was about 11 watts from what I remember; I only used the B3-ish charger once to know most people will chuck the charger into the corner only to collect dust.
Sorry.