When topping up a battery, what level should it be filled to?

When topping up a battery, it is important to fill it to just above the cell plates. This ensures that the electrolyte covers the plates sufficiently to allow for proper chemical reactions during battery operation while also providing enough space for expansion of the electrolyte as it heats up.

Filling the battery just above the plates prevents the risk of overfilling, which could cause electrolyte to spill out during charging due to gassing. This can also help in minimizing the exposure of the cell plates to air, which could lead to sulfation and reduce the battery's efficiency. Additionally, maintaining the correct level contributes to maximizing the battery's lifespan and performance.

Positioning the fluid level too high (like to the top of the battery) can lead to spills, and filling it too low (like just below the cell plates or halfway between the plates) can expose parts of the plates to air, risking damage and decreased battery functionality. Thus, filling to just above the cell plates is the ideal practice for maintaining battery health.