1/8 RC LiPo battery: 4S vs 6S, capacity, C rating and connector
For a 1/8 RC car, choosing a LiPo pack is not simply a matter of selecting the highest capacity. The voltage supported by the electronics, the available battery-tray space, the current the pack can deliver and the connector must all match. This guide uses the published specifications of products currently available in the catalogue.
4S or 6S: start with compatibility, never with power
A 4S pack is rated at 14.8 V. The Traxxas 4S LiPo packs listed here are intended, according to their product pages, for MAXX, X-MAXX and Unlimited Desert Racer applications. A vehicle designed for 4S must remain on 4S. Moving to 6S when the ESC, motor and vehicle manual do not permit it exposes the electronics to a voltage for which they were not designed.
6S is a different power system, not simply an option for more speed. The catalogue currently has no active 6S LiPo pack for a 1/8 RC car: do not choose a 6S charger, connector or pack on the assumption that it will be compatible. Always check the voltage specified by the vehicle and ESC manufacturer.
5000 mAh or 6700 mAh: runtime, weight and space
Capacity represents stored energy. With the same setup, 6700 mAh provides more runtime than 5000 mAh, but you must also check the tray dimensions and accept the additional weight.
- Traxxas TRX-2889X: 4S, 14.8 V, 5000 mAh, 25C and a Traxxas iD connector. Its published size is 155 x 34 x 45 mm. Choose it when a more compact pack is required in a MAXX, X-MAXX or Unlimited Desert application.
- Traxxas TRX-2890X: 4S, 14.8 V, 6700 mAh, 25C and an iD connector. Its published dimensions are 175 x 53 x 45 mm. It suits a model that accepts this size when the aim is longer sessions with an X-MAXX 8S or Unlimited Desert Racer.
Understanding a 25C discharge rating
The C rating estimates the continuous current available: capacity in amp-hours multiplied by C. A 5000 mAh pack equals 5 Ah; at 25C, its theoretical current is therefore 125 A. A 6700 mAh pack equals 6.7 Ah; at 25C, this represents 167.5 A. This calculation helps compare packs, but it never replaces the limits set by the ESC, motor and vehicle wiring.
Both 4S packs above are rated at 25C. The choice between 5000 and 6700 mAh should therefore be made first on runtime and physical fit, not on the assumption that one pack is automatically better for aggressive driving.
The connector: stay within the charging ecosystem
The TRX-2889X and TRX-2890X use the Traxxas iD connector. The Traxxas EZ-Peak Plus TRX-2981G is specified for iD LiPo packs up to 4S, with 75 W and 8 A. It identifies an iD battery and configures charging automatically. This is the simplest pairing for an existing Traxxas iD setup.
Two practical choices
- You need a compact 4S iD pack: choose the TRX-2889X after confirming that the 155 x 34 x 45 mm format fits the tray.
- You prioritise runtime and have a compatible tray: choose the TRX-2890X and its 6700 mAh, while accounting for its 175 x 53 x 45 mm dimensions.
Charge on a suitable surface, use the LiPo mode and balancing procedure recommended by the charger, then store packs according to the manufacturer's instructions. For charger selection, see our guide on choosing an RC LiPo charger.
