Save time, money and the environment by ensuring that your battery is always fully charged. 1. Avoid flat batteries and get a car that always starts. Getting to your car on a cold morning and discovering that it won’t start because the battery is flat is as infuriating as it is common, especially in winter. Sub-zero temperatures weaken the battery more than most people realize. At -18°C, even a new battery can only perform at 40% of its original capacity. Cold weather also i