I use optima red top... Lots of guys run yellow top especially those without alternators. I often put a jump box on the batt to charge it up a little between rounds (usually just once on a race day) if I notice volts at idle on the low side. Many racers use a charger after every round but then you need to mess with a generator or find an outlet. I would also suspect the starter or quality of the connections especially grounds both at the motor and the battery.. When hot all are less efficient from higher resistance

-Chris