Marine Batteries 101

I could use some help regarding marine batteries. I understand the concept of having starting batteries and house batteries. If I'm installing starting batteries, should I have a dedicated battery for each engine or will one work? I know this is elementary but I'm just starting out and I want to do this right. I'd rather ask a bunch of dumb questions here and then do it properly than do what I think is right and find out later that it isn't correct.
Any advice would be greatly appreciated.

You should have a dedicated battery for each engine.

I agree with N4712 but have a boat that doesn't have 2 start batteries.

When I bought my boat, it came with one 8D start for both engines and two 8D batteries for the house bank. It's worked well for 37 years, but I prefer redundancy.

I changed the house bank to 6 golf cart 6V batteries, but kept the single 8D for the start battery figuring I had the ability to tie the house and start together if needed for redundancy. Since the 8D is overkill to start a Perkins 4.236, my plan is to replace the 8D start battery with two Group 31 start batteries when the 8D gives up the ghost.

I plan to use combiners to keep all the batteries charged as needed.

Battery setups on a boat is another area where people have different opinions. I favor one large bank of deep cell batteries that does everything, serves as house bank and starts all three engines. In my case I have a single 12 volt battery which is isolated and which can be used to start the generator.

The benefit of one large bank is that the bank is charged from all sources so that if an engine is running it is charging the house bank, not just its starter battery.

In my case the isolated battery is stored under the helm and operates the radios. It has a separate charger.

The benefit of one large bank is that the bank is charged from all sources so that if an engine is running it is charging the house bank, not just its starter battery.

However IF the batts are all run down fore some reason the noisemaker will be the only hope of getting the engines started after long hours of charging.

The simplest is to have a start batt that seamlessly joins the house with engine start.

At the yacht shop for hundreds of dollars , or at the local RV supply for about $18.00

Well isn't this a timely post for me. I don't have a clue what the PO was doing with the batteries on ASD. I have 3-8D batteries. 2-start and I think one house. The house is connected directly to the stbd start battery, yet all the connections for the house are on this stbd start battery!

Becuase I have an old 80-90's era charger, my batteries are getting fried.

So the solution. I am installing a newer more up-to-date charger, 30 amps instead of 50amps. I am seperating the three batteries. The start will only be used for start and the house will not be connected to any other batteries. I will install a battery isolator, so when I start my stbd engine, it will charge the house bank but not the start battery if it doesn't need it. I will also be switching to 6Vdc golf cart batteries for the house. Lastly, I will be rearranging the battery charger to where it will charge the two start batteries and the house banck seperatly and removing the charger from the genset start battery. I will also be installing a watering system for all my batteries. Lots of work and $$ to spend.

Hi Bennett

As house bank and engine starters... Been using four (4) wet cell Group 31 Deep Cell Marine Batts from "BatteryPlus" store for years. High quality, inexpensive, no problems, easy to maintain, charge quickly, and collectively supply plenty of power. Also have a gen set Group 27 starter batt... and... a completely independent Group 27 deep-cell/starter combo batt that's in separate batt box. I always keep it 100% charged in wait for if all else fails, as a safety feature!

We're very efficient on how elect power is used aboard boat. At anchor for long as we want gen set usually runs about .75 hr in morn and .75 hr in eve. That keeps all bats charged, AC refrigerator cool, food cooked, coffee perked, water hot, 2 computers/2 cell-phones charged, recharged batts on low level cabin lights... and what ever else we need... like occasionally portable power tool batts charged. Oh, and that includes our 5 mile walkie talkies.

Cost for whole set up from BatteriesPlus was under $650... inc all batts, 2 battery testers, a trickle charger for independent safety batt and its seperate batt box. Over 5 years now and it all is still going strong!

To the OP's question: You can set up a twin engine boat where both engines share a starting bank. Tiara does this on most all their boats. This can cause issues, especially if bank is weak and you are running computer controlled engines. Starting the second engine can dip volts and cause first engine to stall.

If running old style mechanical injection engines, nothing wrong with engines sharing a bank. You can get redundancy by being able to parallel to the house bank.

Genset can also share the main engine starting bank. In this case I usually disable the gennie charging circuit, as batts are more accurately charged by house charger.

And second that about grp 31's. That's the go-to batt size for systems I set up.

FF said:

The benefit of one large bank is that the bank is charged from all sources so that if an engine is running it is charging the house bank, not just its starter battery.

However IF the batts are all run down fore some reason the noisemaker will be the only hope of getting the engines started after long hours of charging.

The simplest is to have a start batt that seamlessly joins the house with engine start.

At the yacht shop for hundreds of dollars , or at the local RV supply for about $18.00

Click to expand...

FF,

What are you talking about for $18.00 that combines the start batt with the house batts?

parallel switch or solenoid....

N4712 said:

You should have a dedicated battery for each engine.

Click to expand...

Only one of many ways to wire a boat..none is best...and only some are bad in certain setups....

Here is one way to do it.

Have one starting bank. The alternator from one engine to charge it.

Have a house bank charged by the other engine.

Have an ACR or combiner that will automatically charge the needed bank.

Have a parallel switch that will throw all the power where needed.

For a belt and suspenders approach, have a separate battery just for starting the generator. If all else fails it will start the generator to charge the batteries.

The method of having a seamless system that required ZERO effort on your part is to copy what15,000,000 RVers have been doing, for 6 decades at least.

The trick is to install a high quality keyed start switch , and purchase a solenoid from the RV store.
Cole Hersey makes nice marine key switches with ACC built in..

The solenoid is connected (use big wires ), between the start and house batts.

The ACC terminal on the key switch (thin wire) is the control for the solenoid .

ACC is only powered when in the RUN position , just what is required to charge the house batts.

Secure the engine with the key and the merge circuit is opened , so the batts stay isolated.

If a pull cable stops the engine , the oil pressure alarm sounding should be enough to get you to turn off the key switch.

Done, perhaps depending on the dockside battery charger.

IF its a single output charger every few weeks or so of just cottage sitting the key should be turned to ACC and left there overnight , or at least for visiting hours.

This will energize the solenoid and charge the Start batt from the house charger.

A better charger will have 2 circuits and this is not needed.

The usual RV solenoid is 75A , so a pair handles almost every alternator out put.

Also available in Marine from Cole Hersey at 200A , but sadly not for $18.00

FF said:

The usual RV solenoid is 75A , so a pair handles almost every alternator out put.

Also available in Marine from Cole Hersey at 200A , but sadly not for $18.00

Click to expand...

Thanks FF! When you mention "a pair," are you talking about two per engine run in parallel or something else? How would they be run?

I'm all about simplifying the process. I live in fear of that one time when I forget to throw my switch from "both" to "house".....Although I guess I shouldn't be too concerned as I have a separate start battery for the gennie.

Moonstruck said:

Here is one way to do it.

Have one starting bank. The alternator from one engine to charge it.

Have a house bank charged by the other engine.

Have an ACR or combiner that will automatically charge the needed bank.

Have a parallel switch that will throw all the power where needed.

For a belt and suspenders approach, have a separate battery just for starting the generator. If all else fails it will start the generator to charge the batteries.

Click to expand...

This is how mine was set up, and is again, after un-doing some mistakes by the PO.

It does depend on a smart 100A inverter/charger with two outputs for the starting and house bank, but most modern chargers have that.

I've added a 2nd charger for the genset battery, only because I had it sitting around anyway. Maybe one day I'll add an emergency battery up on the flybridge to power the electronics. Then I'll wire the 2nd output of the 2nd charger to that. The house bank is 6v GC batteries, the starting bank is two group 31s and the genset starter is one group 31.

Anyway, my point is, this is normally a hands-off arrangement. I have a manual override to activate the combiner when needed. If that fails I can power the charger from the genset, or even the portable Honda 2000. And I keep a pair of jumper cables as a last resort.

Ski in NC said:

To the OP's question: You can set up a twin engine boat where both engines share a starting bank. Tiara does this on most all their boats. This can cause issues, especially if bank is weak and you are running computer controlled engines. Starting the second engine can dip volts and cause first engine to stall.

If running old style mechanical injection engines, nothing wrong with engines sharing a bank. You can get redundancy by being able to parallel to the house bank.

.

Click to expand...

Exactly how mine is set up with mechanical engines.

Bennett, need more info!!!
What kind of boat, what use do you give it?


There are so many ways depending on your needs.
I have a 34LRC in the tropics. That for us means....genset!!! Only way to power two a/c units. I do mostly weekend trips, couple of week long twice a year.
I like having one bat per engine, plus my house. My genset is completely independent. My DC usage is pretty light, my big amp eater is the Lectrasan.
I could go the whole weeked on my batteries, but rarely do, genset runs every night. Just had a set of AGM batteries sent to battery heaven due to a faulty ignition switch. Back with regular lead acid, economical and easy to keep.