Battery Drainage Issues

jlombardo · Jun 19, 2024

I have a 1998 Mainship Sedan Bridge 31 with twin Marine Power 5.7 Liter gas engines. Each engine has an Interstate deep cycle 31 battery. There is 1 main 12v circuit that can be switched between batteries. My issue is that I have added several devices (remote spotlight Wi-Fi, video camera) that are always on and when I am out fishing drifting (GPS on) or anchored with the motors off for an extended period of time, my one battery drains to the point where it will not start the starboard motor. I assume that all the always on devices that I added are on the starboard battery. This is pre-battery on/off switch. I do see similar output from the alternators on both engines in the 13+ range.

My question is do you think it would make a significant difference if I added a second Interstate 31 to the starboard side in parallel? Would the alternator and battery charger handle this?

Any input would be greatly appreciated.

John

Delta Riverat · Jun 19, 2024

If it was me I would add a third battery to power the "house" loads only and leave the engine batteries to only start the engines.

Comodave · Jun 19, 2024

Delta Riverat said:
If it was me I would add a third battery to power the "house" loads only and leave the engine batteries to only start the engines.

Yup. Absolutely. Then just use the current batteries for starting the engines.

RT Firefly · Jun 19, 2024

Greetings,
Mr. jl. Deep cycle batteries WILL start your engines BUT they are not designed for that. As Mr. DR suggests, third battery dedicated to house loads. THIS is the place for a deep cycle. Deep Cycle vs. Starting Batteries: Understanding the Difference

When it comes time to replace those deep cycle batteries that are currently (HAH!) being used to start your engines, I would replace them with "regular" starting batteries. OK to keep using the deep cycles for starting but...

ranger58sb · Jun 20, 2024

jlombardo said:
My question is do you think it would make a significant difference if I added a second Interstate 31 to the starboard side in parallel? Would the alternator and battery charger handle this?

That's generally the easiest wiring solution to a boat set up like yours. It's a very common battery architecture, and given space you can usually add one or sometimes two batteries to each bank to deal with house (non-engine) loads.

Your charger manual will tell you if it's satisfactory, but generally increasing a bank size by one battery -- or increasing both banks by one battery -- won't make too much difference of you routinely recharge from shore power anyway.

Other recommendations given here would likely involve new or revised wiring into the electrical panel, not a huge problem but not one you would likely want to try yourself. (That's a guess, based on the level of your question.) Technically it'd be a nifty battery architecture, but most U.S. built powerboats don't start that way and it's a bit more work (than it's worth, in my mind) to make the modifications.

The Interstate "deep cycle" batteries you have are more likely dual purpose batteries... reality versus labelling... and that style should be fine for your purposes.

You might review your add-ons, spread those load over both battery banks...

-Chris

jlombardo · Jun 20, 2024

Delta Riverat said:
If it was me I would add a third battery to power the "house" loads only and leave the engine batteries to only start the engines.

In this configuration, what would charge the house battery while underway?

John

ABfish · Jun 20, 2024

jlombardo said:
In this configuration, what would charge the house battery while underway?

John

In this situation, I've used a Minn Kota alternator charger. Once your starting battery is sufficiently charged, it will redirect the charge to your house battery. It also isolates the house battery from the starting battery.

Delta Riverat · Jun 20, 2024

I would consider a big LiFePO4 for the house loads. Depending on your usage you may be able to simply charge it at the dock and have plenty for the job. A 280 AH will last 28 hours at 10 Amp draw no connection to the alternators, just a dedicated charger. A 60A charger will bring it from flat to full charge in 4 and a half hours.

ranger58sb · Jun 20, 2024

Delta Riverat said:
I would consider a big LiFePO4 for the house loads. Depending on your usage you may be able to simply charge it at the dock and have plenty for the job. A 280 AH will last 28 hours at 10 Amp draw no connection to the alternators, just a dedicated charger. A 60A charger will bring it from flat to full charge in 4 and a half hours.

Could be an elegant solution in some architectures, but I think OP's current set-up -- two dual-purpose banks, with each bank handling both engine-start and house load service -- doesn't really lend itself to that being a quick and easy change.

I think I still haven't seen many (any?) LiFePO4 batteries that are advertised as ideal for engine starting (or thruster service)?

-Chris

Delta Riverat · Jun 20, 2024

He said there was a switch to select from port or starboard battery to run the house. Should be easy to find the house feed, it's right there at the switch.

ranger58sb · Jun 21, 2024

Delta Riverat said:
He said there was a switch to select from port or starboard battery to run the house. Should be easy to find the house feed, it's right there at the switch.

As I understand him, both banks are starting batteries, one for each engine. The switch only selects which star battery powers the other DC loads.

I think.

That's a typical Luhrs Group/Mainship battery architecture.

-Chris

Battery Drainage Issues

jlombardo

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Delta Riverat

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Comodave

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RT Firefly

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ranger58sb

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jlombardo

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ABfish

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Delta Riverat

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ranger58sb

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Delta Riverat

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