Battery Switch Advice

A split-charge relay. There are hundreds on the market.

I like these.

http://www.balmar.net/PDF/Duo%20Charge%20Manual.pdf

Very good question.

Does you gen-set know which battery is lowest?

Do your batteries know which to drain first?

Smart packs work really well and they are there for safety reasons too.

Leave the battery switch on both while the engines are running.

While you are anchored for 8 hours do you leave the Generator running with the battery charger on? If yes, then leave engine battery switch on both as the battery charger should keep them charged.

If no Generator running, turn the battery switch to 1 battery after shutting the engines off. When ready to start the engines turn the battery switch to the other battery, start engines (1 at a time with a couple minutes between cranking the second one), once both engines are running switch battery switch to both.

If the generator has it's own battery and it's isolated, you should always be able to start that and get the battery charger going to charge the other 2 batteries, it may take an hour to a couple to charge the engine batteries enough to start the engines.

If you plan on anchoring a lot, your best bet might be to install another battery bank and run ALL of the house electrical items off of it instead of the engine batteries. Wire in a battery isolator to charge both banks automatically from the engines (without backfeeding either bank), and from the battery charger be able to charge both banks as well.

Engine Start Batts have a lot of CCA (Cold Cranking Amps) that does what it says on the label and go BRUMP when you hit the starter key. Lots of Amps very fast.

House bank Batts have a S-L-O-W discharge cycle to run lights and such. The 2 are very different types and used in different ways.

Don't mix them up.

My understanding (as written in my Carver manual) is that not only with either battery start either engine, but ordinarily when the engines are running the alternator will charge both batteries connected to the switch regardless if it is set to 1, 2, both or off position.

Our usual practice is to leave our batt switch set to either 1 or 2. If we run the stereo and other stuff all day, and fail to start the engines set on one battery, then we'll switch to both and have never had a problem.

The one time we had a problem was when we had accidentally left the switch to both, ran down both batteries (it was a long day), and had to run the genset (which has its own battery) to charge the 2 main batt's.

We also have an additional 2 bank of 6 volt batteries wired serially to run TV, DVD, video games and netbooks. They also get charged from the batt charger.

Whether using BAT1 or BAT2 will depend if they are all starting batteries or if the separate banks are starting/deep cycle. Daytime anchoring equipment should run off of the deep cycle.

If they are all starting batteries (such as mine are), then it doesn't matter. I almost always have the genset running while out at anchor, so I leave mine in the BOTH position. For the times I anchor without running the genset, I switch to BAT2, just to ensure I have one starting bank ready. Also, my genset has an isolated battery for it's operation and that will run my onboard battery charger.

The way I read it in the manual for carver is battery switch should be on 1 or 2 do not use both. Both on the battery swich is a parallel for emergency use when you have a weak battery. When you run the engine you switch to 1 or 2 to charge the batteries do not switch when running the engine or you will mess up your alternator. Shut your engine down before switching the battery switch.

The reason for that manual suggestion is the same reason there are warnings on plastic bags and rear view mirrors.

The alternator will not be harmed by charging two batteries. Where did that idea come from?

Where you have the 1/2/both switch is generally on boats that may well not have a generator or the operator is likely to not use it (usually 35' and under). Once you have a generator involved it's almost a moot point. Leave it on both. That way you're charging and draining all banks evenly, and all banks are available for starting.

Very common on smaller boats that will often not have a gen and all batteries (generally only 2) are used for starting and house. That way you can save one battery while at anchor with the fridge and stereo on.

It wouldn't be the first boat modified that way.


Without a clever regulator to (no pun intended) conduct the duet of two alternators, one will undoubtedly take the day off and let the other guy do all the work but no real harm is likely. I agree that a second switch is the way to go but that doesn't prevent the same issues that a single switch may or may not create.

I have a 2001 carver with gen, 3 batteries one battery is for gen only with it's own switch. The other 2 batteries are for the engines and house usage. I have a battery switch bank 1, bank 2 and both. When switch is on bank 1, or bank 2, it will start both engines and house battery for the boat. Bank 1 or bank 2 the one not being used is isolated so it really on reserve. When batteries are weak you turn the switch to both position battery bank 1 and battery bank 2 are connected in parallel both batteries are being use.This is used when your batteries are weak. It says to switch to either bank 1 or bank 2 when the engines are running. When you are running the engines use bank 1 one day and use bank 2 another day it will keep them charge, of course if you use your gen the charger will be charging both batteries all the time.

No, it's cheap. Remember, you're mostly dealing with day boats, not boats that will be on many extended cruises. If there is a short in a system that requires it to be brought off line (unusual occurance) you simply disconnect that lead. On these boats a gen or even a battery charger is often an option. On several 35 footers your near the top end of a system that is designed for a 16' runabout.