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# Calculating battery charging time

## Calculating battery charging time

(OP)
I have a Samsung Galaxy Note 10.1 and it has a non-removable 7000mAh Lithium-ion battery. Its wall adapter output is rated at 5V and 2A max. According to my calculations, if I feed 7Ah battery with 2A current, it should take 3.5 hours to get fully charged. But my tablet gets charged in about 1 hour! How is this possible? Can anyone please explain why is this happening?

I am trying to design a powerbank circuit but theoretical calculation are showing that its single cell Lithium-ion 10Ah battery will take 10 hours to charge from a typical smartphone adapter rated at 5V and 1A max. But observing the above mentioned case, I have started to think if there is something wrong with my approach or calculations. Please help!

Replies continue below

### RE: Calculating battery charging time

(OP)
I have to rely on tablet's charge indicator to know the battery status.

### RE: Calculating battery charging time

Almost every tablet built measures the voltage of the battery. You can compare the voltage with the discharge curve to determine where you are in the state of charge. You are probably at >50% charge, given operating margins, etc. The battery has to last some number of years per the tablets design life, so it's unlikely that the tablet allows the battery to actually get to anywhere close to 0% charge. Note that battery manufacturers and tablet manufacturers have different motivations and requirements for state of charge. The battery guy wants to show the best possible capacity, and will allow the voltage to drop to a low, but plausible, voltage. The tablet manufacturer will want to cut off the battery before it operates unreliably, and customers complain about lost data, etc.

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### RE: Calculating battery charging time

(OP)
Yes that actually makes sense. Thanks!

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