Unusual battery arrangement.

[chal]

This is the battery switching setup in a new-to-me Westerly boat. I haven't seen wiring like this before. I know it was professionally installed when the new engine was installed c2006. It all seems well done and in good condition. There are two batteries, which I'm about to replace, one connected to each isolator.As you can see, both the starter motor and the house circuit are connected to one of the switches, so there is no way of connecting one without the other. You can have one or other batteries, or both, but always with everything or nothing running. So far as I know the previous owner just turned both switches on and that was it, in which case there might as well be only a single switch.

Mostly what the batteries do is start the engine. The boat has very little in the way of electrical systems - a few lights and a water pump - and lives in a marina with shore power so the batteries can be kept well-charged.

My plan is to replace the batteries with two new AGM leisure batteries as these are leak proof and maintenance free and claim to be equally good for starting and general power supply. Is there any benefit to treating them as separate batteries and trying to alternate which one gets used for what? I could change the wiring so one became the house battery and the other the starting battery, but given the way they will be used, I doubt if there would be much benefit. The existing switches are the type you have to operate with a key, which I'm not particularly keen on. I own a new, expensive rotary on-off switch and am inclined to use that as a replacement for them. It would make everything nice and simple, and make it easy to charge them both at the same time. Is there any obvious drawback to doing that?

 

[Pete7]

I think changing it to rotary 1/2/both/off is a good idea. We snapped the key on a charter boat fitted with those sorts of alternators. Thankfully it remained switched on.

 

[chal]

The switch I have is just a simple on-off - one of these. So, no either or both option for the batteries.

 

[PaulRainbow]

That's a daft system.

Replace the switches with something better, either two of the BlueSea ones you have, or a couple of these https://www.amazon.co.uk/Marinco-69-701-Switch-Battery-48/dp/B005DUUL9W?th=1

One switch for the engine, one for domestics. You could use one of the key switches currently fitted as an emergency parallel switch, keep the key hanging near the switches, but not in place.

If you can fit a moderately sized engine starter battery, you could parallel the 2 AGMs for the domestic bank.

Fit a Victron VSR betwen the two banks for simple, no user input, charging of all batteries.

 

[VicS]

This is the battery switching setup in a new-to-me Westerly boat. I haven't seen wiring like this before. I know it was professionally installed when the new engine was installed c2006. It all seems well done and in good condition. There are two batteries, which I'm about to replace, one connected to each isolator.As you can see, both the starter motor and the house circuit are connected to one of the switches, so there is no way of connecting one without the other. You can have one or other batteries, or both, but always with everything or nothing running. So far as I know the previous owner just turned both switches on and that was it, in which case there might as well be only a single switch.

Mostly what the batteries do is start the engine. The boat has very little in the way of electrical systems - a few lights and a water pump - and lives in a marina with shore power so the batteries can be kept well-charged.

My plan is to replace the batteries with two new AGM leisure batteries as these are leak proof and maintenance free and claim to be equally good for starting and general power supply. Is there any benefit to treating them as separate batteries and trying to alternate which one gets used for what? I could change the wiring so one became the house battery and the other the starting battery, but given the way they will be used, I doubt if there would be much benefit. The existing switches are the type you have to operate with a key, which I'm not particularly keen on. I own a new, expensive rotary on-off switch and am inclined to use that as a replacement for them. It would make everything nice and simple, and make it easy to charge them both at the same time. Is there any obvious drawback to doing that?

It is a perfectly usable system
You can use it to select which battery is in use in just the same way as would with a 1, 2, BOTH, OFF switch

There would be no significant advantage in replacing the switches with a 1, 2, both switch . It would just involve a load of butchery to fit one with nothing to gain.
(A voltmeter and/or an ammeter will help you know when the engine start battery is recharged)

I suggest the following procedure:

Switch no 1 battery ON, Start the engine. ( assuming no1 is your engine start battery)
Allow the battery to recharge then switch ON battery no 2 and switch OFF no1

Keep no 2 battery ON until you next want to start the engine, or switching both OFF before leaving the boat.

Avoid keeping both batteries ON except in an emergency. It is a route to having both batteries discharged if you are not careful

 

[PabloPicasso]

I think changing it to rotary 1/2/both/off is a good idea. We snapped the key on a charter boat fitted with those sorts of alternators. Thankfully it remained switched on.

I carry a spare key. They are really very cheap.

Those 12B0 switches are often left in the wrong position.