iphone battery useless after ios 8.4

Since installing ios 8.4 on my iphone 5s, the phone is practically useless, using approx 1% of battery power for every minute i'm using it - ie looking at it, making notes.

My phone is dead by lunch.

I have visited the Genius Bar - and can't get back for another 10 days.

I have turned off background app refresh, turned off almost all location services, I have rebooted as a new iphone and installed a mere 3 apps which I know from the last year do not have battery draining issues; yet I still

1) Have an incredibly hot battery at random times - often after a period of no use.

2) Have a battery is next to pointless.

Other posts have suggested a roll back to ios 8.3 - is there a way to do this?

Or have apple stuffed my phone?

Any help gratefully received. I have itunes running on Windows 8 if I need itunes to help reset.

Thanks