Auxilary Battery Problem

[zrt600]

1999 GMC Serria 2500 with the aux battery. On a four hour trip I can smell what I describe as "rotten eggs" in the cap. Opening the hood the aux battery is spewing smoke through the vents, battery was very hot to the touch, also dead.

 

Any ideas as what may of caused this?

 

Thank you all.

[bronyaur]

The battery is shot. Get it out of there ASAP. Once they start smelling like rotten eggs there's no saving them. The smell is caused by sulphur dioxide, which is often caused by overcharging. Since it is your auxiliary battery, I would check your battery separator or isolator, or whatever setup you have, but it's quite possible the battery just died.

 

[jnpaddison]

what is your alternator charging at ??