Why Do Car Batteries Fail In Heat More Than Cold?

All 12-volt car batteries have six separate compartments (cells)…and inside each separate compartment, there are thin metal plates. In a wet battery, there are many lead metal plates, thinly separated by materials. When (and if) those metal plates touch each other…it creates an electrical short, which begins car battery failure. 

So when it’s super hot, those thinly separated metal plates will expand and can touch each other (especially when the materials separating the metal plates degrade), opening up easier paths for those plates to touch. This creates mild shorting when the metal plates inside the cells touch. Thus, the battery begins to die. A lot of high heat (Texas in summer) accelerates this. But in Cape Cod, there’s not as much summer heat, so car batteries last longer.

That’s usually a latent result of high heat from the summer (expansion, degradation of materials separating those thinly separated metal plates), or inactivity of driving (the alternator recharges a car battery when you drive). For example, when cold temperatures reach 15 degrees Fahrenheit for two straight nights back-to-back, the metal plate failure inside those cells hits a tipping point…and everyone’s car battery that’s near dying from effects of battery age and heat will tip and die at once. That’s why everyone’s battery goes in cold snaps (a latent effect from age and summer heat).

Right before the extreme heat of summer and the extreme cold of winter. Failing to prepare…is preparing to fail.