wireing battery"s in parallel

[BrianG]

This is why I personally do not suggest parallel connections. In order to safely hook batteries in parallel, they must be very close in voltage, preferably exact. I would charge them both up to get a fresh peak and then hook them together.

But, judging by your description, you probably shorted both batteries. Parallel connection is done by hooking the + wires together and the - wires together. Sounds like you hooked the + and - together, which shorted the batteries. This generated a HUGE amount of current; enough to melt the plugs.