Galaxy Tab S2 9.7 reboot loop when battery is at 25%

[Nja123]

My mum's tab s2 is just over a year old and has started a reboot loop since September. I clear the hidden cache and it will be okay for a couple of days but the n it plays starts rebooting again.  When it reboots the battery power can suddenly drop from 25% to 3% in a second. Does anyone have any other suggestions as I don't think it is right that I should be having to do this all the time. Also I'm concerned that it might be battery issue. Thank you.

[FC360]

I had mine repaired a few months ago as I remembered I had a support plan, apparently it was a issue with the mezz unit-if usb fpcb, mainboard and the battery which all got replaced and so far I haven't had the issue. I'm not sure how expensive this would be to repair without some kind of repair/support plan. I was also very surprised they still repair these tablets as they're getting on a bit even though it's still able to keep up with some of the new tablets.