How long should I leave the battery on charge?

Depending on the power of battery the timing of charge is 8-10hr. Leaving the battery longer that this time under charge will damage the electrodes in the battery resulting in the decrease of its half-life. Note that, even if you don’t use the battery, make sure it is charged at least once a month. Also, it is normal that some batteries make some sounds when fully charges. This is normal and doesn’t require any action.