How to: manually benchmark your battery health

The health tab in AccuBattery can use partial charges to estimate your battery health, but if the battery charge controller in your phone is inaccurate or you don't have enough historical data, this can lead to difference between actual and displayed health values.

To manually take an as accurate as possible snapshot of the health, follow the next steps:

*There's no need to take the test more than once or twice a month as the capacity shouldn't change that fast. Also charging to a high level is not good for the battery and while the effects of doing the test once in a while are negligible, there's generally no point in doing it more often. 

Simple version:

1. Before going to bed; drain your battery until the phone turns off.
2. Plug in the charger and turn your phone on.
3. Unlock the phone to get past the lock screen at least once after you start the phone.
4. Leave it charging overnight (beyond when it shows 100%).
5. The next morning check the bottom of the charging tab for the 'estimated capacity'. (If your phone suffers from early shutdowns and you couldn't start the benchmark from 0% then you need to check the 'Charged' > 'Total' block on the charging tab to see how much mAh went into the phone).
6. Divide the number by your phone's design capacity to get a health %.

Detailed version:

1. Disable the charge alarm to stop it from bothering you.
2. Drain your battery to the lowest percentage without the device turning itself off. This can be 1% for phones with an accurate battery gauge, or something like 30% if the battery gauge is completely off. If you're unsure at what level this happens, you can discharge until it turns itself off, plug in the power and restart the device. If the phone turns off you should make sure you unlock the lock screen at least once after you reboot it. Otherwise apps may not be allowed to run in the background.
3. Plug in the charger, and verify that AccuBattery is running and counting mAh's.
4. Charge the battery completely. Some phones display 100% while the battery is not fully charged, you can verify this on the charging screen (charge status section) and in the notification, they'll display that the battery is still charging and charge current (in mA) is positive.
5. Topping off the battery can take up to 1-2 hours depending on how wrong or fake the "100%" mark is. The level displayed is determined by the device manufacturer - a side effect of the fast charging war, the lower you set the 100% display level, the faster the user thinks the device charges. Example: 10 minutes, for a Nexus 4 that doesn't cheat with battery %. 
6. Try not to use the phone while running a benchmark charge, measuring the current in mA is more accurate while there's no / low CPU load and variance in power usage.
7. After a full charge charge, click the cycle in the history tab. You'll be taken to the CHARGING TAB where you'll see how many mAh's can be added to the battery at most in the "Charged" section (in the 'Total' block). For devices with an inaccurate 100% indicator or devices that shut off at for example 30%, you need to look at this section to see how much mAh your phone can hold. For devices that do accurately display 0-100% then the battery capacity estimate block at the bottom of the charging tab tries to pro-rate for the start percentage, so you can check the mAh numbers here as well if you didn't start off at the absolute minimum level. Due to charging from empty to completely full this is the most accurate estimate for 'estimated capacity', better than what you get from the health tab.
8. Divide the estimated capacity by your design capacity to get a health % out of it. 

In rare cases these factors below may lead to bad data being reported or cause issues. For most people it's not necessary and you can just ignore it but if you want to be certain you've done everything you can:

1. Use a regular wired charger and not one of those super fast chargers that came with the phone in case it has special logic that controls when the charging stops. A wireless charger may also lead to broken sessions if the contact isn't good or the phone is accidentally moved.

2. If your phone has adaptive charging in the system settings turn it off. A couple of devices (Pixel branded devices seem to be overrepresented among them) will report incorrect charging current and/or charging states during adaptive charging.

3. If you have the paid version of the app you can enable our overlay (any of the 3 overlays will do) while you do the benchmark. Most phones will not kill an app when it's running an overlay so if your phone sometimes kills our app and breaks off our session data this may help if whitelisting us in the system settings doesn't. This is just a temporary workaround though because many apps (especially banking apps) do not let you run overlays over them.