charging a 12V battery that is down to 7.5V

[JonE]

I rescued an old Yuasa 45AH 325A ?aircraft battery from inlaws' house.
I've tried to put it onto a Lidl smartcharger but it won't even start on its ramping cheeses display. 
What would you advise? 7.5V reading, but its one of those ones with no fill possible.
I have a standard car battery charger too. The battery says do not exceed 4.2A charge or 10 hours charge, but I'd have thought that something tiny would be much better?

[Reckless Rat]

I think you'll find it has failed under constant kineticism + excessive discharge

[JohnD]

Set of jumpleads off the car onto the battery, let car idle for 15-20min then stick battery charger back on, it will probably have enough in it then for the electronics to regognise it

[JonE]

thanks - nothing to lose John, so will try before considering consigning to skip...!