Many remote-control (RC) cars are powered by battery packs containing rechargeable nickel cadmium (NiCad) or nickel metal hydride (NiMH) cells. The speed of your RC car is limited by the voltage and amperes of the car's engine. You can't simply increase the voltage to the engine because you may damage it, and replacing an RC engine can be expensive. However, you can get more speed from your RC car if you change your NiCad or NiMH battery pack to a lithium polymer (LiPo) pack. LiPo cells produce three times the voltage of a NiCad or NiMH cell: 3.6 volts compared to 1.2 volts, so you need only one third of the cells to power your device. Fewer cells mean less weight, which converts to more speed.
Check the voltage requirement needed to power your RC engine. The label on the engine will provide this information.
Get a LiPo battery pack and charger from your electrical or hobby store. Ensure you get a LiPo pack that's the same or similar voltage as the input voltage of the RC engine. LiPo packs are available that will produce a range of voltages, but they are always a multiple of 3.6, the output voltage from each LiPo cell. If you find you can't exactly match the engine's voltage to a LiPo battery pack, then choose one that's the closest. For example, if your RC engine operates on 10 volts, then get a LiPo pack that produces 10.8 volts: 3.6 multiplied by three equals 10.8 volts. The extra 0.8 volts won't damage your engine.
Disconnect the red positive wire extending from the battery pack from the switching device. It's usually attached using a small screw, so use a suitably-sized screwdriver to undo the screw and release the wire. Using a screwdriver, disconnect the black negative wire extending from the battery pack from the negative terminal of the RC engine. Remove the existing battery pack from your RC car.
Put the LiPo battery pack into the RC car. You will find it's smaller and weighs a lot less than the one you removed. Attach the black positive wire extending from the battery onto the negative terminal of the RC engine using a screwdriver. Attach the red wire from the battery pack onto the switching device using a screwdriver.
Test the speed of your RC car using your LiPo battery pack. You will find that it goes faster and that the battery lasts longer between charges.
If your LiPo battery pack doesn't have wires extending from it, you can get a wired connector from the electrical or hobby store that connects to the pack and onto the RC engine.