It is annoying when the laptop battery becomes less and less useful, where it doesn’t hold the charge it once held. It is even more annoying to try to navigate between all the different sellers using mAh to describe the battery replacement for something that is likely expressed as mWh on your original OEM battery or as determined by the free application BatteryCare. The conversion is simple.
I am a novice at this, however, after several different Internet searches, I have figured out a set of equations to make the conversion. For example, an original OEM Dell laptop battery reported that it had 85000 mWh. However, it no longer held a charge. A replacement offered on eBay was rated at 7800 mAh. The laptop battery voltage in both cases is 11.1V.
The first step is to calculate milliampere-hour (mAh) to ampere-hour (Ah).
Ah = mAh/1000
Ah = 7800/1000
Ah = 7.8
Calculate Watt-hour (Wh) using the Ah value calculated above.
Wh = Ah * V
Wh = 7.8 * 11.1
Wh = 86.58
Then convert Watt-hour (Wh) to milliwatt-hour (mWh).
mWh = Wh * 1000
mWh = 86.58 * 1000
mWh = 86580
So, 7800 mAh = 86580 mWh … that is if my calculations are correct. This is set of equations I used to purchase the replacement battery.