that's a nicad battery. it certainly needs re wiring as the connector is missing. you need a female mini tamiya connector to fix that. now the battery is out dated tech as is the tamiya connector and the way to go would be to rewire the gun to use Deans connectors and buy a 7.4volt lipo battery of at least 1400mha capacity of roughly the same dimensions as the nicad battery. Down side of this you need to be able to solder (not that difficult but will require a soldering iron) and you will need a new smart charger for the lipo (battery and charger going to be minimum £40.00) . best option to start with is to spend a couple of quid get a female tamyia connector, fit it to the battery and charge it and see if it can still hold a charge.