I installed lollipop on mine using Kies and it's fine, smooth, fast, but battery life is horrendous
I heard all about the S4/S5 battery life being 2nd to none, I got longer out of my old Lumia, even with the screen turned down to only millimetres away from lowest, I can sit and watch the battery % drop one by one
Battery usage info tells me it's the screen with the highest use, everything else is barely touching it - I can't turn the screen down any lower unless I lived in a cave, at night, with an owl
Read all the battery saving tips kicking about the net, and tbh, if I wanted a phone with no sensors working, no wifi, barely readable screen, I'd have bought a potato