@applee Thanks for the ideas, I think there might be a couple of things going on, but the battery is an issue with this device tbh. I have replaced and can do so again, but I think that this device is well known for having a rubbish battery life as in losing its capacity quite quickly even when the device was new.
It was plugged in on mains at the time, but will try at 100% and see how that goes, although it was working fine on Android prior to flashing it. I did have a few issues when installing UT, the time it succeeded weirdly the interface on my computer was saying still transferring files to the device, but the device itself was asking me to run through the initial setup at that point. So tempted to try and get it installed cleanly.
Thanks for the link too.