A car battery is made of three components, lead, sulfuric acid and water, over time the acid erodes the lead and the lead is the main charging part of a battery that is why vehicle batteries are called lead-acid
what causes the battery light to on a 2005 ford expedition to come on?
Sulfuric acid fumes escaping from the battery.
A few causes that will make the Battery Light come on are: 1. Faulty Battery 2. Loose Battery Connection 3. Battery is not Charging, ie. Faulty Alternator
The battery for the battery backup is weak maybe
Cranking the car or starting the car in cold weather can wear out a car battery. You can also wear out the battery by turning the starter over without fuel in the tank.
Usually a battery will leak because of overvoltage, overtemperature or a bad battery cell.
a flat battery
Sulfuric acid fumes escaping from the battery causes this corrosion.
Failed battery, or alternator is overcharging.
Your battery is weak, or your your alternator is not charging battery.
Dead cell in battery or something is on pulling power from the battery.
Waiting for the battery to drain completely to extend battery life.