I popped un Ultima in mine, they are pricy, huge current available. Spins the motor up soo quick. I have had one before, and it didn't last 3 years. I keep it on trickle charge now, i think it was my fault as i let it go totally dead.
I have used Lucas many times in the past, and had no issues with them at all ProParts is a good place for them. Take your old one along, or even a photo of the part number on the label, so they can find one that fits. They are very helpful. Pro Parts, Stratfield Park, 13, Elettra Ave, Waterlooville PO7 7XN