Why is the weak point of a lander the battery?

The battery is the most delicate component on a lander. Landers can’t shut down if there is a low battery. The electronics must be at minimum temperatures. So there are heaters to keep the electronics warm. As the solar panels get covered with dust and winter arrives, the lander starts to use more power to keep warm than it is getting from the meager daylight that makes it through the dust. Once the battery runs down, the electronics get too cold to operate, and the whole system dies. Even if the solar panels recharge the battery somewhat, there is nothing to tell the system to reboot.