Asmand1,
Don't waste your money on a lantern battery. These days, they are usually nothing more than eight D-cells in a tuna can.
Goto Pratt Hobbies website and buy one of his power bricks. for about $25 you get the battery pack and a charger. He does a good job of sourcing good ni-cads. Mine is three years old now, and still good for over 100 launches on a single charge. It can sink enough current to pull in five automotive relays firing five copperheads simultaneously.
You can also look into getting an RC car battery pack and charger at Toys-r-us or rodeo shark for about $20. They are usually 7.2 or 9.6 v though, but plenty for solar igniters.