You left your tablet switched off for half a year, and it didn't discharge at all... right. 1 to 2 per cent over 24 hours doesn't equate to fully discharged in 7 days.
4% drain in 3 minutes after power up would depend on the circumstances prior to power up. If you hadn't used the device in a few days, then the battery would have discharged somewhat anyway (as already explained), plus it would have been doing overtime downloading whatever it needed to do since it's last power up eg updates, emails, etc
If you're still worrying, then try the below troubleshooting suggestions.
●Hard reset
With the device powered up, Hold the Volume down button and Power button simultaneously for 10 seconds. The screen will go off. Continue to hold buttons until the device vibrates and the Samsung logo appears. Release buttons. Device will reboot. Once done, please check if the issue is resolved.
● Cache partition wipe
Plug into a working PC or laptop or other Samsung device
https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/● Safe mode
To rule out any 3rd party apps or customisations that might be causing your issues, please boot to Safe Mode.
To get to Safe Mode - Long press Power button, long press Power off icon, tap Safe mode icon. (When booted into Safe mode you may need to turn off flight mode as it sometimes enables itself). Monitor your battery behaviour. If the issue is fixed, then you know it's one of your 3rd party apps or customisations that were the culprit. It's then up to you to determine which one by a process of elimination.
https://www.samsung.com/ph/support/mobile-devices/how-to-use-safe-mode-on-samsung-galaxy-device/There's a battery diagnostic in your Samsung members app. Just head to the Support section and tap on Diagnostics. Report back with result.
Take a look at your battery stats, too, for an indication of battery consumption.
Finally, the nuclear option. A full factory reset. Ensure you backup first.
