Replacing batteries

We're back from our long weekend on Jubilee. One job I did was to renew the domestic battery bank. The original setup was five 110 Ah leisure batteries in parallel, charged while cruising from an alternator separate from the engine battery alternator, and controlled by a Sterling device. The load on this was the domestic 12V circuits, plus a 3kW pure sine wave inverter feeding a mains fridge. The wiring was not really done in the best way for evening out the charge/discharge of all five batteries: the inverter, for example, was connected across the battery at one end of the five.


(Sorry about the poor photo - I used flash in the "after" shot - the inverter's fat leads are connected to the far battery)

I will replace the mains fridge as soon as Ally and Ben have finished their spell of marina living. Until then, I will allow the fridge to be powered only while the engine is running (unless on mains hook-up, of course). I think five domestic batteries excessive, especially for cruising. If the load requirement needs five batteries I think that the alternator will struggle to keep them charged.

So I've replaced the original five with just three. These were provided by the former owner - as I'd shown some knowledge (!) of batteries etc. when he was showing me the boat, we agreed that he'd let me install them and not him.


I've wired them up in a way which I hope will even out the charging/load, and thus prolong their life. From the second photo, you should be able to see that all three + terminals are connected directly to each other, similarly with all three - terminals. I've connected the inverter between the + terminal of one battery and the - terminal of another; I've done the same with the alternator leads.

Problem 1: I discovered that there are two different sizes of connecting posts - one large, for the inverter leads; and one small, for everything else. This dictated to some extent the wiring, and one post, the + terminal nearest the camera, has too many connections for the nut to hold them down securely. I must do something about this. Probably the best thing is to move one of the leads onto another connecting post.

Problem 2: The positive lead from the Sterling alternator control box won't reach further than the middle battery position (that's the one with five red leads going to it - I left two batteries in the box unconnected as spacers) and I had to file the connector's hole larger to make it fit the post.

Problem 3: The two batteries left unconnected in the box will die unless I keep them charged up. I brought home the three batteries I removed so as to charge and test them. Thinking about it now, I should have brought the other two home to look after, as the indicator windows on these two show green, signifying that they are still in good condition.

Problem 4: I don't know how to draw directly onto the screen, so I can't easily provide a wiring diagram. (I could draw on paper and photograph it, but not now. Too late.)