If you have some room above the batteries then one of these works great. Fill it with distilled water then put spout in cell opening and push down. Water will flow until electrolyte covers vent hole in spout automatically shutting off flow.
Around $12 at Walmart.
Unlike a "Watering System" you can also use it on all your other batteries on cars, trucks, etc. Just hard to use on small lawn/garden and motorcycle batteries as the spout is too large.
These were a staple item in all "Gas Stations" up until Self Service took over.
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"A wise man can change his mind. A fool never will." (Japanese Proverb)
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2018 Flagstaff Micro Lite 25BDS
2023 f-150 SCREW XLT 3.5 Ecoboost (The result of a $68,000 oil change
)