Li-ion batteries

A solar garden light teardown shows why casually replacing nickel-metal hydride batteries with lithium-ion cells can be dangerous. The circuit lacks the charging and protection features lithium cells require, meaning a Li-ion swap can lead to overcharging, overheating or fire. The example serves as a warning to tinkerers to match battery chemistry to a device's charging circuitry rather than assuming rechargeable cells are interchangeable.