I has this same issue. After a couple of hundred miles from new would not turn on. LBS fitted new wiring loom then they couldnt get it turn off. Turned out to be prob with lights accordng to LBS. Was a Vado SL4.
I sometimes do 90 mins without using assistance just lights / bluetooth and it doesnt drop more than 1 or 2 %. Vado 4 sl bought Sept 2020. UK owner. Bike kept in gararge.
Yes the battery is built in and you have to at least part remove the motor to change. Bike is currently at Specialized dealership being looked at under warrenty.
Vado SL 4 Turbo. 6 weeks old 240 miles 3 charge cycles. Placed on charge and all seemed normal. Went to use in morning and everything dead. No response whats so ever. Plugged charger back in and nothing. Just had call from shop and they say they have ordered a new battery and wireing harness...