Ever since we took posession on the boat, we've been having problems with our battery bank. Well, the problems didn't actually surface until, two weeks in, we stayed in Cropredy for a day to meet fello boaters and for the first time, didn't charge the batteries for eight or so hours, as we had been for the preceding days. The fridge was the indicator: we were playing host to that well known double-act, Bones and Maffi when it sounded like there was a hamster trapped in the fridge. This, as we came to realise, indicated that the batteries had dropped to a voltage too low to support the fridge's heat pump. The length and small diameter of the power cables supplying the fridge wouldn't have helped matters either; although the fridge stopped working at 12.1 volts measured at the batteries, the voltage the fridge was receiving- reduced by the resistance of the wires- were even less.
This went on for months. Every time we were unable to run the batteries during the day, we'd not have a fridge. In fact even after a full charge, it would be merely 8 hours before we could no longer run the fridge. While cruising it wasn't such a problem; we charged them enough most days. Once we arrived in Cambridge the issue became more pressing. Finally able to spend time to get the wole bank apart andtest them individually, James found none of them to be obviously deficient, and we resigned ourselves that we needed new ones. However, we decided that before we did so ( we couldn't yet afford to buy them anyway) a Canal World thread was required! As always, there were many helpful answers, but the breakthrough came when James realised that they were actually wired up incorrectly. This page (from SmartGuage) explains why. Basically we need them to be wired up so that they act as a single large cell, and this wasn't how it was done. Three of the five were never being fully charged or discharged, which wasn't ideal.
So during his half term, James rewired them. And we charged them up fully in Upware last week, only to return from the pub to a very sulphurous smell, and a very unhealthy battery, as described in a recent post! This was clearly a dud one, probably bringing the whole bank down.
And things are definitely improved. the bank holds a ~12.7V charge for much longer than it ever did. We just have to get back into the habit of actually using the fridge, rather than storing milk on the baseplate!