The largest truly portable lithium batteries are increasingly used by remote control (RC) enthusiasts to power their models. Theoretically there's no limit to the number of lithium cells that can be formed into a battery pack, so RC models are getting more powerful. For example, you only need to build a battery pack that contains 10 regular-sized lithium cells and the pack produces 37 volts and up to 24 ampere-hours. No other rechargeable battery comes close to this. Naturally, there is a finite limit as to when a battery stops being portable.
During 2007, the largest lithium car battery cell was developed, designed for use in the hybrid Toyota Prius. The battery contains 63 individual cells that produce 7 kilowatts of energy, enough to help the car achieve in excess of 125 mpg. Lithium battery developments continue, but the weight-to-power ratio and the space the battery needs are important considerations as to how large a lithium car battery can get.
Auto-racing has long been responsible for many of the developments seen in today's gas-fueled cars. The same may be the case for the development of lithium batteries. Two large lithium batteries have been developed for use in a couple of race cars competing in the 2011 Dakar Rally. One produces 24 kilowatts while the other produces 53 kilowatts. The batteries are understood to power the cars for 90 miles and 240 miles, respectfully. A regenerative braking system helps keep the battery charged and solar panels also assist recharging.
During 2009, the largest currently recorded lithium battery was built to power a hybrid bus. The battery weighs 771 pounds and produces 180 kilowatts of power. However, despite the battery's size and power, it can only produce enough energy to operate the bus on pure battery power for a short distance, but the bus's braking system automatically helps recharge the battery every time the brakes are applied.