Charging and discharging a battery at the same time

[CWatters]

Is it me or...

I was surprised to discover quite a few people think it's possible to charge and discharge a battery at exactly the same time. For example laptop users think the battery is simultaneously being charged by a charger and discharged by the processor at the same time. In reality the charger is powering the processor in this situation, the battery is only being charged. At least it is when the processor load is less than the charger capacity. If the load briefly exceeds the charger capacity the battery supplies the excess. But even then its only ever being charged or discharged never both at exactly the same time. Its not actually possible to charge and discharge a battery at exactly the same time because current cannot go both ways down a wire at the same time.

... unless of course I'm missing something ?

 

[Baluncore]

... unless of course I'm missing something ?

You are technically correct, but for the complexity that, since a "battery of cells" can have a Battery Management Controller, some cells may be charging, while others are static, or discharging.

Anyhow, your statement is probably true for any single cell.

 

[sophiecentaur]

because current cannot go both ways down a wire at the same time.

Exactly. At any instant, the current into the + terminal can either be flowing in or out. However, there is another important issue of 'management' and that is the Energy flow over a given time. A motor car battery is being charged ('top-up') when the engine is running at sufficient speed and sometimes discharged at low speeds. So the battery capacity (AmpHours) becomes relevant, to see you through all situations.
Same with a laptop computer. Current from the mains power supply will feed the computer's circuits and also charge the battery if needed.
Batteries may be used to 'stabilise' the voltage of a supply to isolate the load from supply voltage fluctuations or drop-outs.

But battery current is only ever flowing one way.