I remember seeing a proceedure for this, can't really remember or if it was for dealers.
Funny I thought the magic button was to charge the 12V battery to pull in the HV contacts,
The fact that you only have 80volts out of 350 means you ain"t going nowhere.
Like Bill said the dc/dc convertor is only to steo down the hv to 12v. I can't imagine
what you would use to charge that monster, except that enginer kit!