My Lenovo Thinkpad T450s has two batteries. Power-Manager's Panel shows remaining time and percentage. Percentage is correctly averaged, but remaining time should be adden (e.g. when one battery will last another 2h, and the other will last 1h, the result should be 3h), but it is not.
It seems like it is averaged as well, resulting in 2h remaining, when one battery is 100% full and the other has 6h remaining.
(this is my first bug report, so please tell me what more information you need, thanks)
I just stumbled on your bug report. I think it well described and good understandable. And finally the screenshot is very helpful too :-)
However I can not reproduce your observations on a Thinkpad T430s with two batteries running Fedora 23 x86_64 with xfce4-power-manager-1.5.2-6.
This isn't easy to test for someone who doesn't have access to a system with two batteries... (speaking for myself mostly, but then again, I even don't know anyone with such a system)