If it were my forklift, I would check the static voltage of the battery (12.69 volts is technically a full charge) and complete a load test on the battery first. You can then do voltage drop tests to determine if you are losing voltage through bad positive and negative cables. Also, check for voltage drop at the starter 'S' terminal. There can be a lot of voltage loss between the key switch, neutral safety switch and 'S' terminal. Low voltage to the starter solenoid can cause intermittent starting issues and decreased starter life. I hope that this helps!