Here's a look at a couple of add-on batteries I picked up for my new Team Durango DESC210 RTR. The Onyx Lipo at 4000mah and 25c constant should be a great battery for this lightweight RTR and provide a good weight bias with the lighter battery.
Here's where I got it and some info from Onyx:
FEATURES: Works great for DuraTrax motorcycles as well as other cars, trucks
and boats or any other application requiring a stick pack with a
Deans plug
Protective ABS case has the same dimensions as a six cell NiMH stick
pack
Wired for balancing with JST XH (ElectriFly Style) balance plug
INCLUDES: DuraTrax 4000mAh 7.4V Stick 25C LiPo Battery with Deans Female Ultra
Connector
REQUIRES: Cell balancer such as the Great Planes Equinox Balancer (GPMM3160)
for balance charging
LiPo compatible charger such as the Onyx 230 AC/DC Charger (DTXP4230
SPECS: Capacity: 4000mAh
Number of Cells in Series: 2
Rated Voltage: 7.4V
Continuous Discharge Rate: 25C
Maximum Recommended Charge Current: 1C (4.0 amps)
Pack Dimensions: 5.3 x 1.8 x 0.9" (135 x 45 x 24mm)
Discharge Lead/Connectors: 12AWG 3.9" (100mm) Deans
Balancing Connector: ElectriFly
Weight: 9oz (256g)
Watt Hours: 30Wh