From my research, it is an early'ish bike and I have found several suitable batteries, all around the £200 mark. The big choice, price wise, is the amp hour rating, generally around 10 but, obviously, the higher the rating, the more miles you're going to get per charge. 36v, 250w and 8 - 10 amp hours will give you around 20-22 miles. Perhaps Jerry could have a look at the battery and get the rating off it. Although an early model, it would make a sturdy run around and if you're handy, you can bypass the limiting controls and fit a throttle, thus doing away with the need to peddle at all. 😉
Terry.