Highly recommended product: The Pro-Fill system from Jan Watercraft Products.
I saw the video. Discovery recommended it highly as a great simplification in topping off the water for large battery banks. We have four Trojan T105 Plus batteries, and the two in the back of the area are almost inaccessible.
The battery fill system involves a little float valve that won't accept water when the battery is full.
The janwp.com website, however, is a relic from 2001. It's ASP .net, with a busy layout, overuse of tables, and it's riddled with broken graphics. It has a "Well it worked on my computer" look about it.
As a professional, I always follow the "webmaster" link to provide feedback on that kind of thing.
Want a shocker?
The owner called me. On the phone, to discuss the issues. It turns out that it's an obscure old ASP add-on and the hosting service can't support it properly.
Now I feel obligated to work with him on fixing them.
The product seems to be ideal for inaccessible batteries. It appears that the Jan WP company is spending their time on product support and not wasting time on web marketing. And maybe that's a good thing.
I can't wait to install it.