If you buy a battery the same size/dimensions, and with the terminals in the same positions, it will almost certainly be right for the bike. It is possible if you have a defective battery that that is causing your problem. You should fix that first. It is most commonly just a carby problem, or a fuel tap or filter problem. If you undo the drain screw at the bottom of the carb fuel should run out steadily. If it does, then the next thing is probably to clean the carby jets. You could try a new plug first, which is easier, but probably not under the circumstances the problem.. If it has an auto clutching belt drive, you might find that's playing up, engaging too soon before the revs have got up enough to pull away.. It's a bit hard to tell which often though and so best to eliminate one thing first. You might be able to make an educated guess which is most likely if you have been riding it before, and notice the changed takeoff.. If you take the carb off to clean it, you need to take all the fuel jets out, including a long brass tube that goes from the main jet in the bottom, up to the slide needle.. Clean/blow them and look through them all. Check the connection to the engine is sealing. If it's rubber look for splits, if it's solid metal then it will have a gasket or O ring or both. Metal manifolds, or carbs, can warp where they bolt together, so check for that too, If you do a careful job with the carb and manifold then you can hopefully assume it's not that afterwards, but only if you have been thorough. Then you can move on to the drive system, bad spark-plug or ignition system etc.