battery percentage meaning

[ramonegumpert]

Dear Experts,

My phone battery indicator shows 50% charged.

My question is, assuming the phone needs 5v to operate, what does the 50% mean?

Is it :

1. 50% current / power is left? If so, 50 % of how much amperes / watts?

2. 50% of 5v is left? Unlikely since that would mean too little voltage to operate the phone.

So, basically, I am not sure what does the percent really mean. What is the formula that derives the percentage?

Any clues would be much appreciated.


Sincerely
Ramone

[Borek]

50% of stored energy is left.

[Strat-O]

First off, the battery life remaining indicators are not very accurate, so what is displayed often doesn't show the reality. For example, I've got an ancient RAZR and if it's very low but I only charge it for ten minutes it displays fully charged but only for a short while.

Ideally the indicator would show you 50% if you had a 2000 mAh battery that had 1000 mAh left but that doesn't seem to reflect how the indicators behave.

Strat-O

[ramonegumpert]

Hi Borek and Strat-O, thank you so much for explaining to me.

any idea how mAh can be measured in a circuit?

sincerely
ramone

[Borek]

Battery, resistor, ammeter and clock would be the simplest approach.

[Topher925]

Battery, resistor, ammeter and clock would be the simplest approach.

You can also determine a batteries SOC (state of charge) from its open circuit voltage, although this requires a relatively accurate electrometer.

[Borek]

You can also determine a batteries SOC (state of charge) from its open circuit voltage

Yes and no. While there exists a relationship between potential and state of charge (see Nernsth equation), it works correctly only for a battery that is not damaged. The only sure way of checking the battery is experimental measurement of its capacity.

Not sure why you want to use electrometer, and not a precise voltmeter?