Dud Battery chargers?

[Crazy Dazz]

I have a very flat (but not “dead”) battery that I am trying to charge.
Pulled out my trusty old Projecta that I have had forever, and strted charging it up. Checked back in a few hours and the charger is dead as a dodo.
Pulled out a Arlec I had, it too stated fine and died within an hour. Oh well, old chargers.
Went out and bought a couple of newies. Projecta 4300, and something from Malz called an “Icanic.”
Tried the Malz one, it lasted all of 5 minutes.
The new projecta seemed to be going ok, but left it on several hours (its automatic) charger is now dead and battery worse than ever.

Even had me checking to make sure it’s a 12V battery, and that I had +ve and –ve around the right way.

These have all been 4~6 amp chargers. Should I be going with something bigger?
If the battery has dropped a couple of cells, could that be destroying the chargers? I can’t see how, but FMD FOUR chargers???