Hi There,
I just recieved my new BOSE S1 Pro speaker! GREAT PRODUCT!
I am considering to by en extra battery - but is it possible to charge it externally (outside the speaker)?
Then the speaker it's suddenly beneficial on music festivals etc. as well 
Hope someone can help
Kind Regards
Roland
Denmark
Welcome Roland! Great question that I cannot answer but I'm sure someone will! Enjoy your S1 Pro - they are fantastic, aren't they!!!
There’s no external charger I’m aware of. It has to be charged in the unit. But the good news is the battery is very easy to remove and install.
See this link for more details on the S1 including battery install instructions.