Thanks so much for the help, to everyone who replied. In the unlikely event that in the future, there is someone as stupid as me who has this happen to them... it was so simple to fix. I just connected the battery charger to the positive going into the engine bay relay box. Earthed the negative and kept the charger on 2A (I was paranoid about frying something, because electricity is a total mystery to me and for all I know it is a form of magic). Then I hit the key, after a few moments she started to liven up a bit, and the boot release worked Glad I was able to provide some lulz to you guys, it's a talent of mine. Thanks again.