nimh is better here is a receiver battery that will work our receivers will work with hitec connectors
http://cgi.ebay.com/1400mAh-RECEIVER...em230064488396

and as far as failsafe they all will fit under the body i would go with a duratrax one but i would pick a throttle return spring over a failsafe because if your battery comes unhooked or something it means the failsafe wont work either b/c it is hooked to the battery but a throttle return spring works mechanically once you lose signal it shuts the carb so it dont get any gas and the car dies just make sure you get one that aint to strong for your throttle servo to handle