Bose Soundlink Mini 2 LED blinks red while charging

my friends Bose Soundlink Mini 2 doesn’t charge anymore. This happend from one toe the other day without any obvious reasons. When i try to charge it the Battery LED just blinks red. I ordered a new Battery, but this didn’t fix it. I started to search for shorts on the PCBs inside, but i can’t find any. Does anyone have experience with this and could help me?
Kind Regrads