battery went boom in the 914 today ! Options

[rfuerst911sc]

Haven't driven in the teener in a few weeks and today was an off Friday so good a time as any. Had the battery on a tender so figured I'd be good to go. Battery is aprox. 6 month old conventional wet cell. I unplugged the tender then unclipped the battery clips. Did a quick feel of the battery to make sure it wasn't hot all felt/looked fine. Got in the car, turned the ignition key on and BOOM !!!!! I turned the key off and my mind was racing was that an engine boom or ??? Popped the hood and first thing I noticed was one bank of three battery caps were gone. Looked around a little bit and found it laying on the engine shelf. The cap was OK not cracked or mangled. I wasn't going to risk anything so pulled the battery. Under closer examination the battery case was cracked by the negative terminal. Took the battery to where I purchased it and there was no argument they gave me another new battery. Same type same brand. Put the new battery in the car and she turned over/fired right up like nothing had happened. So defective battery or charging issue or ????