Best backup for starter battery

[afterwork]

I currently have an AGM starter battery connected to my Yanmar engine and Generator. For my house battery, I use a LiFePo4 battery cell bank completely independent from the starter circuit.

My starter battery is still working but it is starting to get a bit old so I am looking at my backup option in case it dies on me when I most needed. I was thinking to just buy an AGM backup and keep it as a drop in replacement in case it dies. But the question with this option is how to keep the backup charged if it’s just forgotten in the locker. I thought of maybe adding a selector switch and switching back and forth between battery uses but this also seems like a tedious option.

I don’t want combine the LifePo4 circuit into the starter in parallel and risk my house battery bank getting damaged.

So I am wondering what are people out there using or recommending as backup? Jump start charger? Extra batteries? Other options?

Thanks for your comments and recommendations

[Bowdrie]

I'm not so sure I'd want just one battery to start both a generator and the engine, (or did I misread what you meant?).
I don't have a generator but do use two Group 31s just as a starting bank.
Personally, I think having two batteries for starting, (with a selector switch with field protection,) is a reasonable minimum.
Yes, my house bank and engine batts are totally isolated from each other by the use of two alternators.

[Renegde_Sailor]

The way I have my boat wired up is I have a dedicated starter battery, house bank, and then a battery in the bow for the anchor windlass, the entire system is 12v.

The cables coming from the battery in the bow are 2/0.

Then in the engine room I have a switch that will let me choose which bank to pull power from to start the engine in case the main dies. The other advantage of having an isolated battery in the bow is that even if the engine will not start and the house bank is flat, I can still get my anchor up and sail if I need to move the boat.

It is always nice to have options.

[afterwork]

Originally Posted by Bowdrie

I'm not so sure I'd want just one battery to start both a generator and the engine, (or did I misread what you meant?).
I don't have a generator but do use two Group 31s just as a starting bank.
Personally, I think having two batteries for starting, (with a selector switch with field protection,) is a reasonable minimum.
Yes, my house bank and engine batts are totally isolated from each other by the use of two alternators.

You understood correctly, the generator and engine are on the same battery. The generator has its own alternator so it will recharge it while its on. Could you elaborate on your concern with this setup?

It seems you two starting batteries is in line with what I was thinking as a backup.

[afterwork]

Originally Posted by Renegde_Sailor

The way I have my boat wired up is I have a dedicated starter battery, house bank, and then a battery in the bow for the anchor windlass, the entire system is 12v.

The cables coming from the battery in the bow are 2/0.

Then in the engine room I have a switch that will let me choose which bank to pull power from to start the engine in case the main dies. The other advantage of having an isolated battery in the bow is that even if the engine will not start and the house bank is flat, I can still get my anchor up and sail if I need to move the boat.

It is always nice to have options.

This is an interesting setup. How are you monitoring or ensuring that the battery in the bow remains charged?

[Renegde_Sailor]

Originally Posted by afterwork

This is an interesting setup. How are you monitoring or ensuring that the battery in the bow remains charged?

There is a disconnect switch up there that stays normally open, then a Victron Orion does the charging by drawing from the other side of the disconnect, and it tells the Cerbo what kind of shape the battery is in, as well I intend to add a shunt to it, I just have not done it yet.

[Ixium]

I carry around a battery booster like from https://ca.gooloo.com

Use it as a power pack for anything else need charging too if need be. But works great as a battery boost

[ranger58sb]

Originally Posted by afterwork

I currently have an AGM starter battery connected to my Yanmar engine and Generator.

My starter battery is still working but it is starting to get a bit old so I am looking at my backup option in case it dies on me when I most needed. I was thinking to just buy an AGM backup and keep it as a drop in replacement in case it dies. But the question with this option is how to keep the backup charged if it’s just forgotten in the locker. I thought of maybe adding a selector switch and switching back and forth between battery uses but this also seems like a tedious option.

So I am wondering what are people out there using or recommending as backup? Jump start charger? Extra batteries? Other options?

Originally Posted by afterwork

You understood correctly, the generator and engine are on the same battery. The generator has its own alternator so it will recharge it while its on. Could you elaborate on your concern with this setup?

One option is just to replace the starting battery now...

And then maybe begin carrying a jump pack (although I dunno what charging requirements that might have).

Another is to install a second battery, use one only for engine starting and use the other only for genset starting. (With or without a selector switch.)

Jumper cables.

-Chris

[Kettlewell]

I replace the start battery about every 5 years before it poops out. Problem solved. But, with my LA house bank I can also use it to start if I need too.

[Tupaia]

Originally Posted by ranger58sb

One option is just to replace the starting battery now...

And then maybe begin carrying a jump pack (although I dunno what charging requirements that might have).

Another is to install a second battery, use one only for engine starting and use the other only for genset starting. (With or without a selector switch.)

Jumper cables.

-Chris

Makes good sense.



Another is to install a second battery, use one only for engine starting and use the other only for genset starting.WITH A SIMPLE VOLTAGE BASED BATTERY COMBINER.

[Turtle Blues]

What is in place now to keep the genset and engine alternators output separated if both are in operation?
As you are considering a 2nd battery now, the Department of Redundancy Departments choice would be to separate the 2 systems and have independent starting capability.
Combining switches (if desired) and isolation for independent shore power charging will add some cost and complexity to this installation.

[Mal Reynolds]

One solution to this: https://www.amazon.com/dp/B0BSCTQDCX...roduct_details

[Jammer]

Originally Posted by ranger58sb

One option is just to replace the starting battery now...

This is the best advice offered in the thread so far. Preventative maintenance beats spares every time.


Having some sort of reasonable and safe mechanism for using the house battery as an emergency source of starting power may be wise, more as a hedge against alternator failure than battery failure. I would suggest a smaller DC-DC charger as one of the simplest and least expensive, since currents involved are low and smaller wires can be used.

[SailingHarmonie]

Sometimes the best answer is to keep it simple.

Use jumper cables to the house battery. Of course this is not something you would do every day, it’s an emergency solution.

In 25 years I have had a starter battery die on me once. The boat had a 24V house bank made of 12V batteries in parallel. Jumping off of one 12 volt battery in the house bank got me home. Obviously not a thing to do routinely, but when the stuff hits the fan you do what needs to be done. The builder of the boat even included the jumper cables as standard equipment.

Of course the real question is if you suspect your start battery is at its end of life, why are you not just replacing it???

[Rohan]

Originally Posted by afterwork

I thought of maybe adding a selector switch and switching back and forth between battery uses but this also seems like a tedious option

A selector switch makes the most sense, but if you don't want that, then why not just start the engine with your house bank? It should be robust enough to handle it. Or am I missing something?

If you keep a separate starter battery, and want to keep it charged, you could also purchase a small solar panel, like 10w or less, that would trickle charge the battery. The cost is minimal.

Something similar to this:

https://www.amazon.com/Sunway-Solar-...df_B01MYVUSRH/