After I collected the boat from having its two domestic batteries replaced, simply because they were "of an age", I noticed that the charge warning light described above was flickering on tick-over, along with the associated warning buzzer, and later found out that the 1800watt inverter was no longer functioning, but instead, alarming. Both these problems were not present before the battery job.
My (or Tom's) first port of call, on discovering this, was to contact the company who installed the batteries, who arranged for a technician to visit the boat, but, didn't rectify the fault, instead diagnosing it as a faulty isolation switch, and as such, not directly related to the job they did. As a result of the professional, but, untested diagnosis, I obtained a replacement switch, and with my own qualifications, decided to visit the boat on Saturday to fit it. The job was very straightforward, but, unfortunately, didn't rectify either fault. With The help of Tom, who is currently using the boat, I conducted a logical fault finding exercise, and found a very definite problem - an arcing, bolted connection, every time the inverter was switched on. This connection was taken apart, cleaned, and put back together using petroleum jelly. Immediately, the inverter now worked exactly as it should, and the engine, when started, no longer showed the charge warning lamp. Bingo! As we were passing through, and on our way to an evening party, I tidied up, and re-checked that everything now worked, which it did.
However, as I started to think about what I had done to fix the problems, doubts started to set in. The bolted joint that had corroded, and stopped the inverter from working, and the charge lamp to stay on, was in fact on the engine start battery positive connection. There was a heavy duty, red cable, bolted to the accessory fixing on the main clamp, that required cleaning. What is bothering me now is why would a cable that would stop the the domestic inverter working be connected to anything that is linked to the positive terminal of the engine start battery? I didn't think of it at the time, I was just thankful I had found, and rectified the faults. Having checked which charge light is which on the instrument panel, I now know it was the start battery circuit warning, which is logical, for the first problem, but why the inverter?
In the past, on the old batteries, we would last quite easily, one overnight stay, using the power sparingly, without any further charging. The engine always started easily the following day, even though we had spent the evening on batteries. This is how it should be, as the engine battery should be isolated from the domestic batteries. I know Tom and Jan are intending to take the boat out now that it isn't showing any fault symptoms, but has somebody, in the past, wired the engine battery to feed the inverter, and if so, why was this not noticed when the domestic battery bank was replaced? Of course there may well be a completely logical explanation why this cable, that is attached to the engine battery, is at the bottom of this, but it will be interesting to know how long the new domestic batteries now last on an overnight stay. I now won't be able to get into any involved investigations until the boat goes out of use for the winter. But, it does appear that everything is now working properly, even if it might be the engine battery that is supplying the inverter! Somebody might know the answer as to why it is connected in this way, before I get a look myself in more detail.