Using the AccuBattery app I'm told that the design capacity of the battery is 4500 mAh, but after 3 significant charging sessions the current capacity is 2095 and has never reached 50% of the design capacity. I've tried contacting AccuBattery and OnePlus to see if I should be trying to exchange this brand new phone given this report. I haven't gotten an answer yet. Does anyone else have any info about OnePlus 8T actual battery capacity or how to deal with this?
This is the answer from AccuBattery support (OnePlus 8T has a dual battery apparently):
Unfortunately there's no solution for this at the moment as the system isn't reporting the values in the correct manner. It looks like more devices with dual batteries have this issue but we currently don't have these devices to test with so we can't figure out the exact underlying problem and build a workaround for it, but the most apparent issue is that the device reports half of the charge current. The health estimate can still be calculated if you do a manual benchmark like this: https://accubattery.zendesk.com/hc/en-us/articles/213575425-How-to-manually-benchmark-your-battery-health but the maximum you will get is half the design capacity so you will need to multiply the mAh estimate by 2 (or change the design capacity so it's half the original value) and make the assumption that the two batteries are used at the same rate; which is probably not what's actually happening (one battery might be used to charged the other for example).