You’ve done a great service (no pun intended 😂) to fellow boaters with these videos Andy. A lot of people are intimidated by it but you explained everything plainly 👍
Its my belief that the water came in via a pipe from the W&E canal at the bottom and then was pumped up to the channel next to the reservoir, flowing inti the reservoir when there was enough and flowing out via either a sluice at the north end to the canal or via an overflow on the southern side.
Invest in a purpose made battery top up bottle. These stop the top up de-ionised water automatically then move onto the next cell. Amazon sell these top up bottles. They're a bit pricey but cheaper than new batteries! I keep ours in a plastic bag tucked away from the engine 'ole to keep the bottle scrupulously clean.
A very interesting vlog. One observation, I was told that the positive solar feed should be on the same battery terminal as the alternator positive feed?
Thats a fair point. I seem to remember that I had run out of terminal space on that battery so used the one next door. I will have another look at that next time I am on the boat.
Those batteries have both threaded bolt and traditional posts. You can always use the other type for extra cable connection capacity, being on the same battery end as the other will be better than being on a different battery.