A forklift uses a battery which varies dependant on the model and brand of the forklift. The battery for each brand of forklift is usually different but some are able to run on batteries similar to car batteries.
A hydrometer is commonly used to test the specific gravity of a forklift battery. This device measures the density of the electrolyte in the battery, which can provide information about the state of charge and health of the battery.
Oxygen and hydrogen
Before charging it.
check the battery
Distilled Water
No, that may damage the battery
Depends what is wrong with it.
Chlorine gas is produced.
Hydrogen
Overcharging by the alternator or if it is connected in reverse polarity.
Usually the battery is too low