Rechargeable battery charging

Hi,
What will the charging current do after the laptop battery is 100% charged? I do understand that the battery will no longer be charged. Conservation of energy states that energy cannot be destroyed. So what happens to the electric energy? Where will it go after 100%?

In general, the current flows to charge a battery because the charger voltage is higher than the battery voltage. As the voltage rises the difference in voltages becomes less so the current drops. In theory, when the two are equal no current flows at all. In the real World, the charge voltage is always higher than the maximum the battery can reach and other measures, such as current limiting or timed cut-off are used to ensure it doesn't get over charged.

Laptops are a special case as the manufacturers push the batery to their limits to make the charging faster, usually the battery pack has a voltage and temperature monitor inside it to maximize the charge rate without risking damage. At full charge, the monitor switches to trickle charge mode to keep the battery "topped up".

As for conserving energy, if the cell is not demanding charge, no current flows so the charger output is present but not being used.

Brian.

Hi Brian,
Thank you for your reply. Can you please explain the charging procedure in a laptop battery in terms of current and voltage for the battery specification: capacity=48Wh, rating=11.1V, min current 4.2Ah rechargeable Li-ion battery.

For this information you must contact the battery manufacturer, only they will know the optimum charging parameters. You can get some clues as to how it works from looking at the data sheets of Li-ion charge control ICs but to be certain you are using your battery in the best way you need to know more about the individual cells inside the pack. It is not possible to derive exact charging details from the figures you quoted which are the ratings for discharge into the laptop.

Brian.