> When I consulted the apple store (Berlin) about it they told it I need not to worry about it

Those people are assholes. Literally.

> Once you notice the battery is swollen or compromised in any way, you should immediately stop using the device. Turn the power off, and above all else, do not charge the device. Once the battery has reached such a point of failure that the battery is swollen, you must assume that all safety mechanisms in the battery are offline. Charging a swollen battery is literally asking for it to turn into an exploding ball of noxious flammable gas right in your living room.

https://www.howtogeek.com/244846/what-to-do-when-your-phone-...