Battery advice for new-to-us Hunter 36...and why did these huge Northstar AGMs die so soon?

Don S/V ILLusion · Oct 8, 2023

Not familiar with these batteries but the specs indicate they are “starting” batteries, not deep cycle, and the charging rate should be up to 14.8V.

We used to have a Freedom 40 charger and don’t recall specifically but don’t think they bulk charge at that voltage.

If they are in fact “start” batteries, I’m surprised they lasted 4 years. And the 20 year age of the charger is spectacular!

Sailgunner · Oct 8, 2023

Switch to 6V golf cart for your house bank. Do you have room for four?

Davidasailor26 · Oct 8, 2023

Without knowing how the previous owner treated the batteries it’s hard to say whether 4 years is good or bad. If they deeply discharged them often and/or left them discharged for any length of time then 4 years is doing pretty well. The 20A charger is a bit undersized for 364 AH of AGM, so that may have contributed to the short lifetime as AGM can be especially sensitive to charging routine.

artboas · Oct 8, 2023

Sailgunner said:
Switch to 6V golf cart for your house bank. Do you have room for four?

I absolutely agree with that.
6v AGM are :
Very reasonably priced
Easy to move & install
Long lasting

Unless you are going the Lithium route, I think this is your best option

JBP-PA · Oct 9, 2023

artboas said:
Unless you are going the Lithium route, I think this is your best option

Lifepo4 batteries are now less expensive than AGM for the same usable AH.

Don S/V ILLusion · Oct 9, 2023

JBP-PA said:
Lifepo4 batteries are now less expensive than AGM for the same usable AH.

Add the cost of a compatible charging system in that equation.

mermike · Oct 9, 2023

Don S/V ILLusion said:
Add the cost of a compatible charging system in that equation.

That may need to be done anyway, as the charging system sounds undersized. If the charging system is inadequate, then the OP should consider the system in its entirety. That may (or may not) point to LFP batteries with an appropriate charger and voltage regulator, depending on his expected use.

dlochner · Oct 9, 2023

AGM batteries are very sensitive to being deeply discharged and left in a partial state of charge for any length of time. The batteries you have are thin-plate batteries which are fairly advanced LA battery technology. While there are many advantages to thin-plate batteries they are very sensitive to being left in a partial state of charge and being left for long periods of time without a float charge. From the technical Manual:

During storage, lead-acid batteries will gradually self- discharge. It is recommended that monobloc SOC be maintained above 12.20 V at all times, while the battery is in storage, in order to avoid irreversible capacity loss. The rate of self-discharge increases with increasing temperature.

The Specs call for a "boost" voltage of 2.35vpc or 14.1 volts, which your alternator is providing. However, if you have a stock internally regulated alternator, it is not providing an adequate charging current, especially if it is a Hitachi alternator on a Yanmar.

One the big advantages of a thin-plate batteries is the ability to absorb a very high charging current which shortens the charging time. The charger you have is woefully inadequate. The batteries have a combined capacity of 360 ah, the charge current should be a minimum of 20% of that, which is 72 amps, even more would be better.

The short story, is your batteries are toast.

Before spending lots of money on new thin plate batteries or upgrading to LFP, do your homework. The battery world is not your father's battery world there have been lots of changes in the technology and understanding of the chemistries. A good place to start is:

Marine How To - DIY for Boaters - Marine How To

For DIY boaters in an attempt to try and keep the sport as affordable & safe as possible. How To articles for sailboats and powerboats.

www.MarineHowTo.com

The technical information for your battery is here:

https://www.northstarbattery.com/media.ashx/nsbbluebatterymanual.pdf

As you begin your education on batteries, feel free to ask your questions here, in "Ask All Sailors" or the Musing with MaineSail forums.

cagreen75 · Oct 9, 2023

If you anchor out often you might consider a large alternator with an external regulator setup to charge the house batteries and a DC to DC charger to charge the engine battery. Solar panels can also be a great addition. Our boat is set up like that. We can go days at anchor without starting the engine to charge the house batteries as long as the sun is shining, and if it is not we can start the engine to charge the batteries. We have converted our ice box to a fridge and also have a portable fridge/freezer that we keep running as a freezer. Our batteries have never gone below 50% charge overnight. Our loads are anchor light, stereo fridge, freezer, and a small amount of lighting in the saloon. Our alternator is a Balmar 120 amp/w external regulator, 2 Lifeline group 31 batteries 210amp/hrs, 45 amp 120-volt battery charger, 2 solar panels 370 watts/with Victron MPPT converter, and group 24 start battery that is charged with a DC to DC 40 amp charger that works only when the engine is running. The DC to DC charger uses the house batteries to charge the start battery. Most boats have the alternator charging the start battery. Since the start battery only starts the engine a large alternator will charge that battery very fast and cut the charge rate down leaving the house bank undercharged. Connecting the alternator to the house bank allows the alternator to use its full capacity to charge the batteries that actually need to be charged. The solar panels on sunny days will keep the batteries at 100% charge while we sail all day with all the items mentioned earlier except the saloon light, plus the Chartplotter, and autopilot. This is not an inexpensive way to do this but it definitely gives me peace of mind that the batteries will stay above 50% overnight and the start battery is always ready to start the engine.

dlochner · Oct 9, 2023

Bolts are standard for batteries made or designed outside of the US. The Northstar batteries use a metric thread. The worst attachments are butterfly nuts, followed closely by those clamps that go on the lead posts.

jssailem · Oct 9, 2023

We have a PacificNW battery maker That I have been using since 2015. They build a variety of lead acid batteries.
Here is an image of their terminal types with the statement of options they use for the 105 Golf Cart style batteries.

As noted above.. the Wing nut options should not be used on a boat. The risk is the wing nut will fail. This has happened on boats with bad results.

Require a Molded In threaded stud. This lets you secure the cable terminal to the stud and use a lock washer between the nut and the cable terminal to lock the nut onto the stud. Cable terminal on first, then a lock nut washer, then the nut. Don’t alter this set up as the nut and the washer are non conductive and will cause a resistance if between the cable terminal and the battery.

BATTERY Special Notes
Optional Terminals:	#3 Wing Nut, Low Profile Wing Nut, Molded in Threaded Stud

Terminal types Key:

shemandr · Oct 9, 2023

Kupe said:
... I have major back issues and already know I'm going to need help getting the Northstars out, …

When I had to remove 4D batteries from my 356 I used a spare 3 part mainsheet with becket and cam. My batteries had web straps, which made it pretty easy to attach the tackle. There was some juggling with length of the travel of the system - did I mention I used the boom to make the lift. It came up easily and with the cam I could stop. It was basically one handed to lift and there was no back strain. I wanted to lift over the combing and swing the boom out over the dock. I couldn’t get the battery that high because of the web straps which were too long. I could have adjusted but by that time some he-men showed up and they weren’t about finesse.
Please don’t risk a back injury!

Ralph Johnstone · Oct 9, 2023

jssailem said:
As noted above.. the Wing nut options should not be used on a boat. The risk is the wing nut will fail.

Everybody is death on wing nut connections. Why ? ? ? ? ?

I have all wing nut connections on my three batteries ................... and replaced all of the wing nuts with nylocks.

dlochner · Oct 9, 2023

Ralph Johnstone said:
Everybody is death on wing nut connections. Why ? ? ? ? ?

I have all wing nut connections on my three batteries ................... and replaced all of the wing nuts with nylocks.

It is nearly impossible to get the correct torque on the nuts, so they loosen from vibration resulting in a poor connection and it goes downhill from there.

Ralph Johnstone · Oct 9, 2023

dlochner said:
It is nearly impossible to get the correct torque on the nuts

Absolutely. That's why you replace the wingy nuts with nylocks or use lock washers. Perhaps my somewhat less than obvious point here is that one should not consider :

☒ a wing nut attachment
vs.

a post attachment

....... as having any bearing on the choice of a battery when the wing nut is so easily replaced.

Tally Ho · Oct 9, 2023

Kupe said:
Wow thanks everyone! Just great advice and experience- thank you! I'm intrigued by the golf-cart battery suggestions. I have major back issues and already know I'm going to need help getting the Northstars out, but I think I could deal with the golf-cart batteries. By coincidence I have a good friend who went that route with his Catalina 35 so I will also pick his brains.

Related question- take a look at this photo of my current installation- the battery terminals and cabling are bolt-in. Is this common? I don't know if this was done during the Northstar installation or did Hunter deliver them that way originally? Wondering if golf-cart batteries can be found that way?

Great stuff gang!

I switched to 6-volt FLA golf cart batteries a few years ago. Fairly inexpensive at Sam’s Club, yet provide 215 AH.
I am a big fan so far…these batts run my lights (all LED), radios (stereo andVHF), autopilot, other instruments (wind, depth), and my refrigerator...and an anchor light overnight.

Simple charging system, solid performance for the way I sail ….lots of day sailing and a few 2-night at anchor trips. I don’t have any solar, and am on shore power whenever not sailing.

I currently only have the 2 GC batteries in a 12-volt bank. Plan to add a starter battery, but so far, I haven’t not been able to start my Yanmar.

YMMV depending on your type of use.

Greg

Don S/V ILLusion · Oct 9, 2023

dlochner said:
It is nearly impossible to get the correct torque on the nuts, so they loosen from vibration resulting in a poor connection and it goes downhill from there.

I can’t help wonder how many people ensure the correct battery connector torque anytime they change a battery. I know I’ve never done that on any car or boat we’ve ever owned regardless of wing nut, bolt or nut. So far, so good…

Battery advice for new-to-us Hunter 36...and why did these huge Northstar AGMs die so soon?

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