[Sado Deomeoon]

My core prime recently installed a new system update, and ever since, the battery has been draining like nobody's business. I charged my phone to 100% at around 3 pm and by 6 am (15 hours later,) it was 18%. Usually, I only charge my phone every week or so, so this is a massive change.
The battery usage says 25% Android system, 25% Android OS and 2% Device idle. Everything else is under 1%.
To clarify, I don't have Bluetooth, location, mobile data, wifi or anything else on. I haven't used my phone since I charged it, and had background data restricted, so I don't think it's apps chewing through the battery.
I tried fiddling with some settings, but the phone still ploughs through the battery life in a few hours. It's not overheating though - in fact, it's not even warm - which makes me suspect that this isn't a hardware issue.

Is this a software issue, or is my battery just bad?
Any help would be massively appreciated.

[Sado Deomeoon]

Update: Turning the phone off, and then turning it back on again appears to have solved this problem.

Strange.