Why are the rover batteries not rechargeable?
The primary source of power for the rover is its 0.22-square meter (1.9-sq-ft) solar panel, and not its batteries. The solar panel is comprised of 13 strings of 18 GaAs (Gallium Arsenide) cells. The power output of the panel at noon on Mars is approximately 16 W (@ 17V). Power from the solar panel alone is sufficient to operate the rover for several hours during the day. In fact the rover was designed primarily to run on solar alone with the batteries providing backup power when needed. The LiSOCL2batteries are arranged in 3 strings of diode-isolated D-cells. They are placed in 3 tubes located at the rear inside the Warm Electronics Box (WEB) next to the RHU’s (Radioisotope Heating Units). These batteries can provide 150 W-hours of energy and supply 8-11 volts of unregulated power to the different converters and regulators attached to the core power bus. There is also a tiny Lithium battery located inside the APXS sensor; it is also not rechargeable. When the power subsystem for the ro
