DENON DSB-100 envaya mini Bluetooth speaker not working?

[obd.tech]

Hi Guys,
i have a DENON DSB-100 envaya mini Bluetooth speaker not working.
This seems to suffer from a pretty common failure and short life span, when i did a google search, lots of unhappy owners which is a shame, as this speaker is supposed to be rather 'Stunning Sounding!'
i managed to take it apart, hoping to find a failed li-on 18650, but it had 3.54v. Looks like it has a protection pcb on the battery.
I charged the battery up directly with my hobby b6 charger, still dead, no response or even battery status led.

Anyone had a play with one of these, that could give me any advice (Preferably not 'Chuck it'  )
i'm very limited in electronics knowledge, but have a few tools  and 10x microscope (nothing i could see visibly damaged)

Would like to fix this great looking little speaker 
Bit of an ask!!?
Thanks in advance for any help