flat battery, tried jump, injector fault

Hi guys,

Wife flattened battery by putting the roof down on her 2005 1.9 megane. We tried jump leads with absolutely not luck at all.

Anyway, currently going to borrow a booster but have put battery on charge and tried again, turned over a little before going flat again and then flashed up 'injector fault' on display.

Im a little concerned about getting it started for there to be something major and am a little weary to try the booster.

So, is it just a case of the battery was flat so its flashing errors or has something been knackered up... Should I just buy a new battery?

Please advise as you guys are pretty clued up.

Cheers

flat battery, tried jump, injector fault