Unlocked htc M7 battery issues

Hi, ever since upgrading my unlocked HTC M7 phone to 5.02 Lollipop, I have been having major issues with charging my phone (among many other issues). My battery will sporadically allow me to charge to 100% using the charger on some days and not at all on other days. I'll have the phone turned off and charging over night for 7+ hours and I will only get 5% total charge. If I reboot multiple times then sometimes my battery charge will jump around. My battery life will drain extremely fast while in standby and I will watch the battery level drop while it is plugged in, as I'm doing right now. I'm not running any intensive apps and in fact have minimal apps installed on my phone. When I get 100% charge I can go an entire day on that charge.

I've tried disabling suspect apps, I've tried wiping the cache and I've tried the so-called battery calibration (vol up + vol up + power button, hold 2+ minutes which restarts phone multiple times). None of this has worked. Is there anything else I can do?

Is it possible to download the old kit Kat Rom from somewhere or is there a fix for this lollipop build? Is there another stable Rom that is very close to lollipop but with all the bugs fixed? I have a tonne of other bugs associated with updating to 5.02. My build number is: 7.17.1540.21

Thanks.