Ok, 5s sounds good.

Would this be too heavy?

Polyquest 5000mAh 5S 25C Lipoly

Spec.
Capacity : 5000mAh
Cell Model: PF 8643150XP
Voltage : 18.5V
Charge Current(2C) : 10.0A
Continous Dis.(25C) : 125.0A
Dimension(mm) : 45.5 * 50.0 * 166
Weight : 639g