I found that topic and because it’s a bug report i assumed not everyone is affected.
My FP2 started it’s life in 2018 with 3-4 days on a full battery with mild use, until some some update degraded it to barely one day without any use. I’ve been in contact with the developer and we’ve done a lot of troubleshooting but never got it back to normal. Somehow it seems to be specific to me because others are not complaining . I guess that’s the downside of community support.
In case you’d want to simulate my use-case:
My phone is mostly idle, 2 SIMs loaded and active. Data connection, wifi, bluetooth and GPS are all off (and only switched on when needed), in case it has a NFC or a fingerprint reader i’d switch that off too. Main usage is an occasional phone call or text message. I used to use the media player a lot for mp3’s (1-2 hours per day) back when the phone still did 3-4 days per charge, but even that use is almost gone now. I do use the calendar and it is important to me, and I sync manually because it only syncs to a server in my network.
I do some CLI work with openvpn and rsync to sync the calendar to my own server and rsync my mp3 collection to the phone, but that’s even less than monthly.
So basically, think about what most people would call low usage and take it even lower .