The Traxxas Rustler 4x4 VXL HD requires a battery that is either a NiMH with 6-9 cells or a LiPo with 2-3 cells. Recommended batteries include the Traxxas Power Cell batteries with the iD logo, such as the 5800 mAh 2s LiPo or the 6400 mAh 3s LiPo, in order to utilise the full power of the vehicle. A suitable charger, such as the EZ-Peak from Traxxas, is also required.

Otherwise this battery with 3000 mAh would be suitable
Traxxas Power Cell (8.40 V, 3000 mAh)

or one size larger
Traxxas battery (7.40 V, 5800 mAh)

With what voltage exactly? Or is it converted by the electronics themselves?