The battery looks unusual. I though it just had a protection circuit at the end but it should have been -ve for the whole flat part
I assume that it is designed so that it can be charged in the lantern (the charging wires come and touch that end only,the -ve and the +ve accordingly)
Hopefully it can also be operated with a standard 18650 battery, loosing the charging capabilities.
I would avoid using any of the inbuilt low cost chargers anyway.
I have a similar one on order, but without any powerbank/charger in it.