Even with knowing the dimensions I had no success. Of course, I found some sellers which sell starting from 1000 pieces. Anyway, the batterie Steve recommended arrived after 15 days. I cannot say anything about the durability, but the device is now working again. Exchange was very easy and did take less then 30 minutes. I am happy to further use the device (sound is even better then a samrtphone).

Hi Steve, thanks for your very helpful answer. I have already searched a while without success (did not know the dimensions).

Thanks for the manual. Does anyone knows where can I buy a replacement battery?