INJURED WAS RIDING A MANBUS WHICH WAS HAVING TROUBLE PULLING A STEEP INCLINE. ANOTHER BUS WAS BROUGHT IN TO AID THE TROUBLED BUS. WHILE ON THE INCLINE THE TROUBLED BUS ROLLED BACKWARDS & STRUC K THE SUMMONED BUS. THE INJURED SAW THAT THEY WERE GOING TO HIT & EXTENDED HIS HAND TO BRACE FOR IMPACT. WHEN THE BUSES HIT THE BATTERY FOR THE BUS SLID & CAUGHT HIS FINGER.