# How much electricity will be used to charge a 4000 mAh battery?

i tried many to search it but cannot find a straight answer

so here is my question how many unit( kwh) of electricity will be used to charge a 4000mAh laptop or any other battery.

if further details are required

its 10.8V li ion

electricity on grid is 240 V 50 Hz.

### 7 Answers

- David FLv 78 years agoFavorite Answer
4000 mA = 4A.

It delivers 4A for one hour, at 10.8 V.

That's 4 x 10.8 = 43.2 Watt hours, or 0.0432 kWh.

It will take 0.0432 "units" (as you call them) to charge the battery, assuming 100% efficiency.

I pay $0.12 per kWh, so to charge that battery would cost me $0.12 x 0.0432 = $0.00518.

If I charged it 10 times, it would cost 5 cents.

- JohnB.Lv 58 years ago
First of all I need to advise you that the reason you couldn't find charging information is that it is dangerous to charge it unless temperature sensors are measuring the temperature of each cell of the battery during the charging process and unless a way to determine when it is fully charged is employed. Each laptop battery contain these circuits. If the internal temperature of any of the cells gets too high it will explode.

assuming it was 100% efficient (not)

If you charged it at 4 amps for an hour it would be full.

If you charged it at 1 amp for 4 hours it would be full.

At 10.8 volts and you charged it at 10.8*4 W for 1 hour it would be full.

If you charged it at 10.8 W for 4 hours it would be full.

Since 1 watt is 1J per hour you can calculate that 10.8*4 j will charge it in 1 hour.

I don't suggest you try to fully charge this battery because you won't be able to tell when it is overcharged. One of the cells may get too hot and, well you know what I said above.

Source(s): Experience with these batteries at TI. They had pictures of one that blew up on a test bench. - Big DaddyLv 78 years ago
mAh is a unit of charge. To determine how much energy (kWh) you need to place the charge in the battery depends on the voltage.

4000 mA hour * 10.8V => 155520 J

or about 0.043 kWh.

- LisaLv 44 years ago
For the best answers, search on this site https://shorturl.im/avg92

You need a battery charger. If you want a good full charge, leave it on over night. If it is fully charged before you disconnect the battery, most chargers automatically go to a 'trickle charge' so you don't harm the battery.

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- RickLv 78 years ago
4 A Hr*10.8 volts=43.2 watt Hr. However, you must also consider the efficiency of the charger. If it's 50%, then the energy required is 86.4 watt Hr.

- billrussell42Lv 78 years ago
4000 mA-hour = 4 amp-hour

4 amp-hour x 10.8 volts = 43 watt-hour = 0.043 kW-hour

But there are losses in the charger circuitry and in the battery itself, so I'd double that number.