The amperage rating of the battery shouldn't be a problem at all. I've run my t-amp off a motorcycle battery quite happily. I didn't hear any sonic improvement with the battery, however, over a good regulated 12v power supply and I didn't want to have to think about recharging.
I have a Pyramid 7Ah regulated power supply that actually puts out 13.8 volts but the t-amp seems to love it. You can pick up new power supplies a pretty good prices on ebay.
I have a Pyramid 7Ah regulated power supply that actually puts out 13.8 volts but the t-amp seems to love it. You can pick up new power supplies a pretty good prices on ebay.