I have 2 (same model) ThinkPad laptops bought a few months apart from Lenovo.com. They both have the same configured hardware but Lenovo may have used different parts as I bought them a few months apart. On the 1st laptop, I installed Fedora. On the 2nd laptop, I installed Debian.

Over the last few months, I have been using a desktop computer and have been "storing" the laptops. Prior to shutting down the laptop, I charge it to 75% and then check battery life 2 months later. A pattern has emerged: the Fedora laptop loses almost zero charge over 2 months. Whereas the Debian laptop is at 5%, 9%, etc.

I am assuming I got a "bad" battery in the Debian laptop. But I was wondering if there is a possibility that Fedora (Red Hat) is doing something that is preventing the battery drain during power off. I know I could test this by installing Fedora on the "Debian laptop" but I'd rather not go to that trouble unless there is some credibility to the idea that Red Hat (Fedora) could be doing something to affect battery drain on power off.

Anybody have any feedback/knowledge about this issue?

Possibly one or other isn't powering off correctly, try using sudo halt -p on both to see if either still loses charge.

Charge them to the same level & turn off. Remove both batteries. Then post in two months.

You could also simply switch the HDs instead of installing different OSes. Get in with a usb key and tidy up, as EFI might be screwed up, but you should be able to check it then.

you might need to swap batteries and test again.

Some notebooks have features which keep on using battery even when off e.g. keep USB ports powered so that it may be used as a power bank, wake up options, etc. Check BIOS settings.

Thank you all for the help. I greatly appreciate it!

I powered on the offending laptop and powered it off with "sudo halt -p"
I'll report back here in a month to see if it helped.

I've been reluctant to open up a modern ThinkPad. I did this with their old ones and swapped hard drives etc. But the new ones don't have easily removable batteries etc so I have been hesitant to mess with this approach, but it's a good idea.

Good idea. But I do have the USB ports set in BIOS to not allow powering devices.

My guess is a bad battery. If it drops from 75% to 9% in two months I see no need to wait a month to check again. I would check the debian laptop after one week then two to check the battery condition.