You can use any U1 battery. The higher the amperage, the more it will deliver and supposedly the better the battery. The big point is it usually costs more because you're paying for the extra lead and/or engineering. The L120 is a 12 volt system, so you COULD put ANY 12 volt battery in there and you'd be fine. The battery tray, however, is designed to fit a U1 form factor without modifying the wiring. What you have to watch out for is that you get a U1 and not a U1R, which has the terminals reversed. In the L120 the positive terminal is on the right (viewed from the drivers seat) when the terminals are toward the front. The U1R group is reversed.
HTH,
Paul
HTH,
Paul