Posted: Mon Jan 04, 2021 10:44pm

I’ve just bought a new starter battery. Everything worked intially then the leisure batteries have drained. Even when having the engine on for 45 minutes nothing happens. I’m desperate to get my heater going. Is there a way to bypass leisure and use starter battery to operate heater?

Posted: Tue Jan 05, 2021 8:54am

With such little detail it is impossible to give you any quality advice. I can give you an answer to your direct question but if you do as i explain it is likely to end with a flat engine battery so you have no way of starting the engine to charge the battery - that is if the problem is not a failed alternator(s) or charging system. I am also relying on your diagnosis that the domestic batteries have drained. The way the lack of domestic power seems to be related to fitting a new engine battery implies the two may be linked so have you left something disconnected or have you unwittingly turned the domestic master switch off. When you start the engine and rev it does the domestic battery voltage jump up a bit as the red light goes out? If you have a single alternator boat ditto for the engine battery. Now your unspecified heater, I trust this is not an ordinary electric heater but is one that burns gas, diesel, or solid fuel. If it is a purely electric heater it is best to consider it as a battery killer and only use it when you have a shoreline connection. The easiest way to do what you want is to put a jump lead between a positive battery terminal on both banks (assuming a conventionally wired boat) but if the problem is shorting cell or cells in one or more domestic batteries then you will damage the new engine battery. So disconnect the negative battery interlink on the domestic battery that has the main domestic positive feed on it. Then put the jump lead between the engine and that domestic batteries positive but that will be against my advice for the reasons I set out above. It would not surprise me if you have left the negative link between engine and domestic battery banks disconnected. If when you were charging for 45 minutes single cells were bubbling, have lost water, or local areas on a battery were getting hot then it indicates a shorting cell. Disconnect that battery form the bank and try charging again but remember to give a reasonable charge takes at least four hours of running at around 1200 rpm (unless its an SL or SR Lister) and to fully charge them well over 10 hours of running. Lack of charging could well be the key but if so you may have ruined the domestic bank.