Kobo Aura Edition 2 battery drain

I have researched this issue and it seems to have been common a few years back. However, I bought a kobo aura 2 recently second hand and it was hardly used. Even if I turn the wifi off, disable auto sync and use no back light, the battery drains very quickly when i turn it off.

It seems the battery "updates" and loses 20 percent when i turn it off and on after some use.

How long should i realistically expect in terms of on screen time for this device? Any tips to solving this issue?

I am using non kobo epubs. Perhaps thats the issue?

Thanks.