My 12V deep cycle marine battery continuously keeps accepting maximum charge of 25A from my Smart Charger. I have left it on charge overnight and it still keeps accepting a charge of 25A - The case gets hot and there is a strong odor of fumes. When removing the charger this battery seems to keep approx 12.7V -- I tested the charger on my car battery and it seems to work fine ( amps dropping and eventually the LED shows FULL. Why is this happening? Have I cooked this battery?

It sounds like the batt. Could be toast. But the true test ? Put a load on the batt. Can it maintain voltage and run out its duty cycle ?