I use Qwik-Fill and so far has worked good for me - I have 3 12V type 27 batteries.
The yellow part replaces the battery caps - and the black fillers are floats - so when the battery is full the floats shut off. The air in the line is pumped out and vents at the battery. The pump has a quick connect for the supply line which traps the water in the system.
I like being able to top off the batteries in a few minutes.
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