Hello,

Recently i had a cell phone battery swell up so i had to replace it. I noticed there was something wrong with the battery that's the only reason i checked it. Since then however, i have looked into this matter a bit more and found that it is not too hard to measure the Ampere Hour capacity of the battery without having to take the battery out for a test. You just need a USB tester that measures at least current or ampere hours.

First, the state of charge curve vs time is not linear as you probably already know. So to test the battery given some relatively small amount of time requires a correlation between the battery curve and the charge current and time. Doing this we can estimate the health of the battery.

The change in state of charge i selected for example was 10 percent. That is, when the phone battery goes up by 10 percent anywhere on the curve. When the battery is being charged, the SOC goes up by 10 percent and by measuring the charge current and time we can estimate the battery health. I like to go by percent because the phone displays this information in the settings/battery section on the phone.

The formula is simple (this is only for a normal charge where the current decreases over time):

t=AhCapacity/ChargeCurrent*SOCfactor (in hours)

The SOCfactor is related to the span in percent change.

For example, for SOC=40 to 50 percent the SOCfactor is 0.1 but for

SOC=70 to 80 percent the SOCfactor is 0.2 which means it takes twice as long to raise the SOC by 10 percent.

So for example if the phone charges up from 40 to 50 percent in 1 hour at a charge current of 300ma then the Ah capacity of the battery must be 3000mAh. If it was charging from 70 to 80 percent however then that would take twice as long to accomplish. This is for the normal non linear charge curve only.

If the current is constant over the entire charge time of 10 percent charge then the formula is very simple:

t=AhCapacity/ChargeCurrent/10

So if the AhCapacity is 3000 and the charge current is 300ma then the time to charge by 10 percent is

t=3000/300/10

which comes out to 1 hour. So you can work this out for the Ampere Hour capacity after measuring the time, current, and noting a 10 percent rise on the phone in the settings/battery section.

Some of those little USB testers measure Ampere Hours so you can just multiply by 10 to get the capacity of the battery.

The most important point though is that if it charges from 40 to 50 percent in 1 hour at 300ma when it is new and 6 months later it charges from 40 to 50 percent in 1/2 hour then the capacity must have went down by 1/2. It may be good to check the battery and probably get a new one.

If anyone wants to add to this feel free. Perhaps any tests you have done.

Recently i had a cell phone battery swell up so i had to replace it. I noticed there was something wrong with the battery that's the only reason i checked it. Since then however, i have looked into this matter a bit more and found that it is not too hard to measure the Ampere Hour capacity of the battery without having to take the battery out for a test. You just need a USB tester that measures at least current or ampere hours.

First, the state of charge curve vs time is not linear as you probably already know. So to test the battery given some relatively small amount of time requires a correlation between the battery curve and the charge current and time. Doing this we can estimate the health of the battery.

The change in state of charge i selected for example was 10 percent. That is, when the phone battery goes up by 10 percent anywhere on the curve. When the battery is being charged, the SOC goes up by 10 percent and by measuring the charge current and time we can estimate the battery health. I like to go by percent because the phone displays this information in the settings/battery section on the phone.

The formula is simple (this is only for a normal charge where the current decreases over time):

t=AhCapacity/ChargeCurrent*SOCfactor (in hours)

The SOCfactor is related to the span in percent change.

For example, for SOC=40 to 50 percent the SOCfactor is 0.1 but for

SOC=70 to 80 percent the SOCfactor is 0.2 which means it takes twice as long to raise the SOC by 10 percent.

So for example if the phone charges up from 40 to 50 percent in 1 hour at a charge current of 300ma then the Ah capacity of the battery must be 3000mAh. If it was charging from 70 to 80 percent however then that would take twice as long to accomplish. This is for the normal non linear charge curve only.

If the current is constant over the entire charge time of 10 percent charge then the formula is very simple:

t=AhCapacity/ChargeCurrent/10

So if the AhCapacity is 3000 and the charge current is 300ma then the time to charge by 10 percent is

t=3000/300/10

which comes out to 1 hour. So you can work this out for the Ampere Hour capacity after measuring the time, current, and noting a 10 percent rise on the phone in the settings/battery section.

Some of those little USB testers measure Ampere Hours so you can just multiply by 10 to get the capacity of the battery.

The most important point though is that if it charges from 40 to 50 percent in 1 hour at 300ma when it is new and 6 months later it charges from 40 to 50 percent in 1/2 hour then the capacity must have went down by 1/2. It may be good to check the battery and probably get a new one.

If anyone wants to add to this feel free. Perhaps any tests you have done.

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