Ford 2002 F650 Owner's Manual page 188

Maintenance and Specifications
Motorcraft maintenance-free batteries do not normally require adding
additional water. However, for severe usage or in high temperature
climates, check the battery electrolyte levels. Refer to the Scheduled
Maintenance Guide for the service interval schedules.
Keep the electrolyte level in each cell up to the "level indicator".
Do not overfill the battery cells.
If the electrolyte level in the battery is low, you can add plain tap water
to the battery, as long as you do not use hard water (water with a high
mineral or alkali content). If possible, however, try to only fill the battery
cells with distilled water. If the battery needs water often, have the
charging system checked.
Make sure the battery cover/shield is reinstalled after the battery
has been cleaned or replaced.
For longer, trouble-free operation, keep the top of the batteries clean
and dry. Also, make certain the battery cables are always tightly fastened
to the battery terminals.
If you see any corrosion on the battery or terminals, remove the cables
from the terminals and clean with a wire brush. You can neutralize the
acid with a solution of baking soda and water.
Batteries normally produce explosive gases which can cause
personal injury. Therefore, do not allow flames, sparks or lighted
substances to come near the battery. When working near the battery,
always shield your face and protect your eyes. Always provide proper
ventilation.
When lifting a plastic-cased battery, excessive pressure on the
end walls could cause acid to flow through the vent caps,
resulting in personal injury and/or damage to the vehicle or battery.
Lift the battery with a battery carrier or with your hands on opposite
corners.
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