I would use caution with those small Traxxas chargers. Recently I received 2 of them with 2 new Rustler VXL's, and even though I have several really nice DC chargers and a 1000watt power supply, I thought I would try them, just because I like testing stuff. BOTH of them did not charge correctly. One of them smelled of burned electronics during charging, and ended up overcharging the battery to 4.29 volts on one cell, and 4.19 volts on the other cell. (Lipos should be charged to no more than 4.20 volts per cell).
The other charger worked one time fine, and charged a battery to 4.18 and 4.19 volts per cell. The second time I tried to use it, it overcharged both cells to 4.26 volts, which is unacceptably overcharged.
If I were you, I would throw those small Traxxas chargers in the garbage immediately before you ruin a good Lipo battery, and pick up a Thunder AC680 charger for $50.00 from HobbyPartz. I have had very good luck with Thunder chargers, and would highly recommend them to anyone on a budget.