Battery charges and passes too quickly. What to do?

I bought a Huawei p9 Lite from Shpock today but something doesn't seem to be right with the battery. When I turned it on it had 100 percent but after an hour it turned off without warning. I then put it on and it just got 30 percent. I always have to work with it because the battery will otherwise run out too quickly or simply switch it off. Have already contacted the seller but he has not yet written back to me, but will probably get back to you later.

Do you know what this is related to and how I can prevent it?

Looking forward to all news!

Do you know what this is related to and how I can prevent it?

Sounds like a possibly "bad" battery - either has been in use for a long time or is faulty - the charging evaluation of the cell phone itself may also be out of order.

It is apparently broken or does not really fit the cell phone. New suitable battery → problem solved.

The battery is flat and should be replaced

https://www.shpock.com/de-de/terms-conditions