Where did you get the phone? It might be that your rom is not completely stock thus unable to ota. More likely if your unit is second hand

I'm using the xiaomi pistons. Great sound but the controls both buttons when pressed reduces volume for some odd reason

This looks quite interesting. Having used their skins on my nexus 4 can be assured of their product's quality and they have good CS too. Might join a bulk if someone is willing to organise.

Try reflashing the rom / kernel. Sometimes bad flashes can have this kind of problems. Battery drain when update also can be caused by bad flashes. Don't know how to describe what a bad flash is lol. It just happens sometimes even after wiping and doing everything properly. Been flashing roms since HTC desire days and whenever I encounter problems like the odd battery drain or the phone is warmer than usual, a reflash usually solves the problem for me.