With the battery removed, inspect the condition of the anti-vibration padding inside a battery carrier. Check the rubber padding inside the battery carrier. Check the rubber padding for damage, hardening of the rubber or bits missing. If this padding is damaged, the battery will rattle around inside the carrier, leading to vibration of the internals, and a shortened battery life.
Place the battery on a flat and safe surface and look at the liquid levels. They should all be above the LOWER LEVEL mark. A 6-volt battery will have 3 cells and a 12-volt battery will have 6 cells, usually with separate filler caps for each cell. Before removing the caps, clean the area around them with a small paintbrush and tissue paper.
The screw type cap has a slot in the top and a rubber washer underneath. If there isn't a screw slot, the cap is of the push in type, use a pair of pliers to gently remove this type of cap with a slight twisting and pulling action.
With the caps removed, top up each call with distilled or de-ionised water to the upper mark shown on the battery. Do not overfill the battery.