Hi @felmue I'm deeply sorry for the late reply.
I can assure you we are looking into this quality matter as it's extremely important to us, we've already made and will continue making changes in our factory / supply to ensure top quality products to our customers.
Regarding the battery, it's an issue came to our awareness regarding the poor soldering (manual soldering) that we looked into and solved, it won't happen in the next products that go to market.
We've showed our engineer the issue and we replicated it, for the long term there is no expected damage to the battery or the circuit so once you've fixed it - it should work properly, no long term effects you need to worry about.
If you are having any troubles or issues, please email me at firstname.lastname@example.org.
Also, I will greatly appreciate it if you could comment here the order/serial number of that product so I could check the batch and the production date if there are any extra issues happened that time.