I've been using the Pro-Fill battery system to keep the water topped off in my four 6 volt batteries for the past 7 years with great results.
I recently replaced the batteries with four new ones and the cell cap openings were 2.7" on-center vs the old ones which were 3.3" on-center. Needless to say, my Pro-Fill system would not fit the new batteries and a new set-up would cost roughly $140.
I called the company and they said I could order new plastic manifolds and use my old caps with the new manifolds. They told me I could order the manifolds from Jan Watercraft Products. I went to their web site and ordered 4 manifolds for $4.50 a piece and selected UPS as the shipping. About an hour later I get a call from a guy at Jan Watercraft telling me they were getting ready to ship my order and noticed I had selected UPS. He said they usually ship them through the post office for around $4 and UPS would cost me $16 and would I mind if they sent them through regular mail. Of course, I went with the $4 method. They mailed them on Aug 2 and I just got them today.
It's nice to deal with a company that went out of their way to save me a few bucks - most places would have gone ahead and sent them UPS.
If you need parts for a Pro-Fill or Quick-Fill battery system, I highly recommend Jan Watercraft Products.