blau, it is simply unscrewing the plugs and adding distilled water so the plates are covered. Only fill to the white plastic marker just above the plates in each cell. I don't disconnect the battery, but that's up to you. I bought a battery water squeeze bottle with a curved discharge tube that allows for precise filling and prevents water spills on top of the battery. It's a good idea to check the battery level every 4-6 months.

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Fred Hoelzle