I'm not the expert on these though I own an ebike. What I do know is that 24V won't get you much speed or distance and are pretty weak with what's out there now.
Lead acid batteries are ok but kind of the Model T of the battery world.
I have a eZee 36 volt geared rear wheel with a 20 amp controller and a 36V 14 ampHr lithium polymer battery. Pretty much top end for the plug and play set up though you can go 48, 60V and 72V battery packs and hub motors and bigger controllers. My set up here in Canada was about $1,800. The company I bought it from is run by a young man who is a leading light for ebikes in the world. He's 30 miles away if I need help.
He's Justin at www.ebikes.ca Homepage of the revolution
Another company is www.emissionsfree.com
The owner is British and has an out standing record for knowledge and product quality plus fair prices. He stands behind his product. He is based in China.
Most of all join www.endless-sphere.com
. Go to the ebike discussion forum and the tech forum. Ask questions because these fellas know all there is to know about ebikes and are constantly pushing the envelope to see what else they can learn.
They will be able to tell you if you can get more out of your Currie and just how to do it.
Put Currie in the search panel on the top of the site. They do tend to be a little vocal if they feel you haven't tried to help yourself before they help you with the problem. It's good natured but they will make sure you get the point.
Hope this helps.