What happens with an overcharged battery?

The effect of overcharging of batteries depends on the type of battery in question. Older battery types can lose capacity when overcharged, but modern batteries are able to retain their quality no matter how many charge cycles they are put through.

Older electronics usually run on battery types like nickel-cadmium or nickel metal hydride. When these batteries are charged too often, they lose their quality and capacity. Newer Lithium-ion or Li-ion batteries, on the other hand, can withstand several hundred charge cycles. They include internal circuitry that makes sure they are never charged beyond full capacity. For this reason, Li-ion batteries are used in most modern phones and laptops.