Typical Duracell D cell is rated at 18,000 mA-hr. It's unbelievable the jump from C cell to D cell. C's are like 7,000 mA-hr. That means a pack of 8 D cells can put out a full amp for 18 hours at 12V. Un-frikin-real.
todd;
i would doubt that eight D cells could maintain that duration, but D cells are beefy indeed.
marc
Seriously, that's the rating on a normal decent (duracell, energizer) D cell. 18 A-hr. You get a lot of bang for the buck on them. Check it out.
Back on this topic, it looks like the way to go is just pick up another SLA or two, I'm headed back to the battery store myself.