It takes about a week of sitting idle for a car battery to drain down to the point where it won't start the engine. If you work from home, or just generally don't drive that much, you should start your car once a week and let it run for 5-10 minutes to maintain the battery as well as circulate engine oil to prevent clogging. Extreme temperatures can also drain your battery, including high heat in the summer and frigid nights in the winter. You'll want to connect a trickle charger during temperature warnings to maintain your battery or drive more often.