after my bootloop, I've now got a 609 serial number - I did a restore from a backup that was about two months old to get phone up and running again - my battery life has definitely improved from what it was before the bootloop and the CPU does not go crazy without reason any more
I see the same wiht my phone since I got it back compared to the Wife's phone.
I can play pokemon go for about 2 hours where she can only get about an hour and a half.
this is us at the same place walking around in the same way.
her GPS drifts more, screen gets hotter and all those fun little things.
when her phone gets down to 15% I am usually on about 20%.
neither of us play while charging anymore, its too risky, phone gets too hot.
we just kill the app, plug it into the powerbanks and chill for 45 min. then play more.
so the older motherboards could possibly be part of the battery drain...