I've had the battery since the beginning of the summer. It probably has about 10 run on it now. You can't beat it for the money.
They also sell a pack that is shaped like the old stick packs. This is one of them (I think they have a few)
I don't own one but people say they work pretty good. I like the one I got though just because it last so long and has good punch.
Just so you know it is tight in the stock RS4 stick pack holders but you can fully clamp it down and the wires clear the bracket.
Just look for batteries with these dimensions or smaller: 137 x 46 x 25mm that have the wires come out in the center of the pack and you should be good.