Exactly, you would be lucky to get half the capacity out draining these slas in half an hour. Thats why I said you will more than double your range with two packs in parallel. You're cutting the load in half- greatly reducing that peukurt effect. For this reason IMO its silly to have two packs available and switch between them using only one at a time.

As an example scroll down and look at the 20, 10, 5, and 1 hour capacities here-
http://www.ragebattery.com/batterystore/SLA-7-12.html

You don't just get X amount of energy out of a battery. As has been said its an electrochemical device, not a simple mechanical one. How you treat it has a big effect on what you can get out of it. A 20 amp load on two paralleled 10ah parallel packs might run three or four times as long as a 20 amp load on a single 10ah pack.

Hate, my Currie took an extra 12v no problems on the stock 24v controller and throttle. A few other people have reported the same thing. Yes there is some extra weight, yes you will have to use your brain and figure out where to put the extra battery. Yes there is wiring to do. You think people would go through the trouble if it weren't worthwhile?

And Currie changes components and designs periodically so its impossible for me to say what worked for me will work for you. But you know what, even if it doesn't work, so what. Go get a 36v throttle and controller if you want the extra speed. If more range is all you want, parallel packs and keep the same voltage. These kinds of mods have been well documented on ES for anybody looking for some help.