battery charging

[dave gone jeepy]

my set up is a bit different two batteries making 24 volts to run my diesel jeep, it has a disconnect on the battery as it's not my day to day drive. i have a 24 volt charger just in case plus the usual 12 volt..
had to shift the jeep as the builders in fixing the quake damage, left the key in the ignition turned on, hence flat battery ( not enough power to start it anyway ).
tried to charge with the newish 24 volt, but as flat as it wouldn't put a charge in, ( was told that was because it is a smart charger ) lol.
disconnected both batteries and put my 12v charger on one, and it is fine drawing 2.5amps and dropping slowly, on the other one the needle bounces to 5 amps and drops to 0 like its pulsing, is it the battery being toast ?
its a few months old a mmmm reconditioned one,

[Crash bandicoot]

if its not drawing current after the initial connection then there is no circut, broken cell...i.e fooked.

as for the 2.5 amp reading could be a dry cell.