Look up PTC or NTC. Dimensions, Color, and Marking are critical to determining values. Try to identify the manufacturer by the logo image on it, and then find an appropriate data sheet.Help, What is this called, and what does it do? it is on the negative side of a battery for a 6v ride-on train (like a power-wheels). Only got 1 recharge out of the battery, now it won't recharge so I ordered a new battery, and the new one doesn't have this on it. What is it? Do I need it?