Since the May Critical Mass ride, I have been powering my sound system with an 18aH Shorai battery. It has generally seemed to work well. The battery weighs just a few pounds and the system sounds good. It tends to last between 40-90 minutes depending on the volume of the music. 

Sadly, after the September ride it appears the battery is not taking a charge.

I called up the company. They said using their batteries for this kind of application isn't advised. It seems likely I over-drained it and in so doing, caused damage. They said it shouldn't be drained below 12.6V and doing the math using my two amps totaling 860W at 75% volume, the battery should have lasted maybe 15 minutes.

Even though they said it wasn't covered by their warranty, they agreed to take it back and try to recover it using their sophisticated charging equipment. If it doesn't work, I am S.O.L.

If I were to get the battery back, I would have to mount a voltmeter to my bike and the party would definitely not last as long. I could run it in parallel with a 36aH battery (which weighs five pounds), but that's very expensive. The battery alone would cost in excess of $350.

Just thought all interested parties should be aware.