A Battery Question regarding Alternator

Newsgroups Archive Prior to 2025
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Hello All,
I have looked through past threads and have a question as I look to replace my batteries.

Background: Currently have 2 banks of 2 deep cycle Size 24 (1 bank for starting and 1 bank for house) that came with the boat. They are older and 1 bank is not great so will replace all. Size 24 just barely fits in the box under the starboard quarter berth (NS 30 Classic).

Plan: Have 1 bank of 3 deep cycle and 1 bank of 1 starter battery. I believe 1 starter battery is sufficient for starting based on seems to be what most of you have. 3 house will increase use of electronics and lights. So choice is flooded at $860 total cost vs AGM at $1594 total battery cost plus another $500 for a charger to accommodate AGM.
Note: I considered lithium BUT too expensive not only for battery but to upgrade systems in the electrical department so won’t be going with lithium.

Question 1: If I go with AGM will I have to upgrade the standard alternator that came with the Westerbeke 27A? The current alternator appears to work well with the current flooded batteries. I understand the charging capacity of AGM is greater so needs more current???

Question 2: Will I really benefit more with AGM considering the added cost?

Any other thoughts or advice please feel free to add it, thank you for your input.

Best regards,
David Godfrey
Nonsuch 30 #145 Classic
RNSYS Nova Scotia

2

To help answer your questions:
Are you on a dock with shore power?
Do you go cruising for several days at a time without shore power?
Do you have a big battery draining load like refrigeration?

Ward Woodruff
N33 #8 Margery
Niantic Bay, CT

3

Good questions that I should have added Ward, thank you.
On a mooring at a yacht club with access to charge up for a day/night when needed.
Cruising for week or 2 without shore power but could probably get shore power if needed.
Not using refrigeration just lights, electronics and occasional windlass.
I’ll also add I will be buying a better battery meter to keep track of the batteries.

David.

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If I was on a mooring, I would definitely have some kind of solar.

Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA

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With the size of the banks you would see improvement if you moved to a 80 amp unregulated alternator and a smart regulator. The stock alternator will struggle to keep the batteries charged in a timely manner.

If you go to AGM you may need to increase your alternator wire size.

An ACR simplifies charging.

I recently replaced my 9 year old flooded Trojan golf cart batteries… With the same. Like you we do not have refrigeration. In 20 years this is the 3rd set of Trojans.

I have seen several bimini mounted paired 50 watt solar panels that preform well.

Cheers Thor

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I endorse Thor’s reply.

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David,
I have a similar situation and have been evaluating multiple options for a couple weeks. It’s a bit dizzying!. Last night I finally made a matrix to compare all the options. I’ve attached my Excel file. For me, I think I’m settling on all AGM with a new charger being the optimal solution. I have 2 house batteries and 1 engine battery. Yes, 1 engine battery is all you need even with flooded Pb-Acid. I don’t believe the AGMs will be a problem for the Westerbeke 27 alternator although that was a definite concern for LiFP04. My use case is I have a slip with shore power and I only do local cruising, usually spending only 2 nights at a time on a mooring or at anchor. I also have a refrigerator which works great but is quite the power hog.
Hope that helps.

George Berntsen
Wave Dancer, N30U #283

(attachments)

Battery options.xlsx (13.7 KB)

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Did you factor battery weight into the installation effort column?

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Ha-Ha, I didn’t but good point. Each of the AGMs is about 70 pounds. Hoping I can get my son to help with the grunt work.
by the way, I forgot to mention in my use case that I have a 100W solar panel and my solar charger is compatible with AGM charging.

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Hey George, thank you for the chart. My chart is similar so we are in same boat so to speak but in Canada prices are a lot higher. All below include taxes.
Do I go with $860 flooded vs $2100 for AGM incl new charger? I’ll be buying a battery monitor as well so that’ll add another $400 to the mix. Balmar vs Xantrex vs Victron - a whole other question on what is best!!!

It should be against the laws of boating economies to not have such a large difference in price for the better system. Anyway to keep everything simple in terms of replacement and cost effective I’m currently leaning towards the flooded but still open to spending more to get more if that is truly the case. To be continued…

David Godfrey
Nonsuch 30 #145 Classic
RNSYS Nova Scotia

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David,
You left out a bit of information. The Westerbeke brochure indicates the standard alternator on a W27 is 50 amps. Is that what you have? If I read correctly you have four group 24 lead acid wet cell deep cycle batteries. You do not state the amp hour ratings for them. Most group 24s are rated at about 75 ah, so I will assume that is that rating. Based on the information provided: no fridge, no auto pilot (?), probably running the engine when using the windlass and assuming an incandescent anchor light, you are likely only using 20 to 25 ah per day unless you have a gigantic stereo system.

Lead acid batteries, either wet cell or AGMs will not give long life if they are regularly discharged below 50%. If you long into the INA site, sign in as a member, go to membership and then select maintenance you will find an article entitled Batteries 101. At page 19 you will find a slide showing the number of charge cycles for different batteries when discharged to 50% and 20%. (Note I think there may be an error on the Firefly battery for the 80% discharge).

The charge acceptance rate of lead acid batteries drops significantly when the batteries get to about 65% state of charge. Here is a link to a Marine How to article

https://marinehowto.com/how-fast-can-an-agm-battery-be-charged/.

It is a bit long but well worth reading. Ia the article a group 31 105 ah AGM (which have a slightly faster charge rate than wet cells) took 5.5 hours to go from 50% to 100% state of charge. A big alternator will not change the equation, however it is generally recommended that an alternator puts out at least 25% of the battery bank size. So a 200 ah battery bank would require a minimum of a 50 amp alternator. A 75 to 80 amp alternator wold better. Having said that I had two 105 ah batteries and then later the two 105 ah for a house bank and a group 24 - 75 ah starter battery that were charge with a 55 amp alternator or a 30 amp shore charger.

Realistically once you leave the dock your alternator would be charging your batteries from 50% to 80% of charge. With your expected load, 100 watts of solar panel would be a very good addition and should largely keep up with the daily demand. Lead acid batteries that are not fully charged on a regular basis gradually loose capacity (walk down). When out cruising if you manage to get to a dock and bring the batteries up to 100% state of charge you will get much longer life from the batteries. By following that approach I got 15 years out of a set of AGM batteries. They still seemed to be fine but I replace them as a matter of caution. The newest set started to walk down but I was able to revive them with a couple of conditioning charges. I am not sure what happened since I treated them pretty much the same as the first set.

The net effect of all of that rambling is that you will normally have about 30% usable capacity with lead acid batteries, about 45 ah from a bank of two 75 ah group 24s, or about two days at anchor without putting a charge back in either by running the engine or using solar power.

Group 24 batteries generally measure 10.25" L x 6.8125" W x 8.875" H (260 x 173 x 225 mm). A Trojan 6 volt golf cart battery is:

Model: T-105

Dimensions Inches (MM) - Length: 10.30in (262) Width: 7.13 (181) Height 11.07 (281)

Terminal Height Inches (mm)1.22 (31) - Bolt 5/16

Weight: 62LBS

They are rated at 225ahs. The extra height was an issue for fitting them under the quarter berths on the 26 but they may fit under the berth on the 30 classic. If you can fit them in they probably give the most amp hours for the dollar of any batteries so long as you look after them. They would certainly meet the requirements of your boat. Because they are 6 volt you would have to wire them in series which would give you a 225 ah 12 volt bank or about 3 days on anchor with no other source of charging. You could have two golf cart batteries for a house bank and a group 24 for starting. Alternatively you could use the house bank for house loads and starting and just have the group 24 as a emergency reserve battery. The start battery would rarely be run down and you could get away with the 50 amp alternator (75 to 80 would still be better). I am with Thor on this and would go with the Trojan golf cart batteries. The maroon ones, not the black ones that you can buy at Costco. I don’t think you will see enough benefit to justify the extra cost of the AGMs unless you don’t look after your batteries. AGMs are sealed and don’t need topping up with water. If you don’t keep wet cell batteries full you will kill them. As long as your shore power charger is a reasonable size you would not need to replace it.

Mark Powers

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I installed Victron BMV 712 last year, with Bluetooth. Bought from Amazon for CA$275, now CA$315… diff is exchange rate and inflation. At the time Balmer didn’t do Bluetooth, maybe now, don’t know. Never looked at the old Victron 600 series, screen too small, bad location, hard to use, no Bluetooth. The new one I check daily when on the boat, because so easy to do. Plus I got a Victron solar controller, also with Bluetooth, and the two units network to each other. Bluetooth makes a big difference.

Hope that helps.
Don

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Hey Mark, I sure wish you lived on this side of the coast! I believe the alternator is the 50A that came with it and the amp hours of the group 24’s is hidden in the well but assume 75 is probably right. They are interstate batteries which I haven’t seen here in Halifax yet so will go with another brand.

Golf cart batteries will not fit in the box, the size 24 height wise is pretty tight as it is so my guess is having to stay the course with 24. I’d have liked 31’s or even 27’s but length becomes a factor. I’ll be taking the batteries out to drill a hole for the solar panel wiring and will have a better idea at that time if I can change out group 24’s to something else.

The battery charger that came with the boat is an old Nautilus-25 (25 amp 2 bank blue in colour) but doesn’t have instructions or anything for me to know anything about it. Nothing on the internet so if anyone has knowledge on them I sure would like to see the instructions and info on it. Because of the unknowns with the Nautilus I am considering a Xantrex 20 or 40Amp charger to make sure the batteries get more modern care in the charger department. Which charger amperage would you suggest Mark? Do you think it right to get a new charger even though current one appears to work?

The solar panel is a flexible 175W by Renogy with an MPPT 30Amp controller. The 30A controller is in case I get another 175W panel. The controller will be attached to the house batteries only because the starter will have limited use and have the alternator or shore power charge to make sure stays right. We aren’t known for sun here in Atlantic but I know there is some sun through the fog. Hoping that will work.

I’m also looking at the Balmar battery monitor system. Going with Balmar because it can work with the deep cycles on 1 bank and the 1 starter battery on the other. I don’t believe the Victron can do that as well from what I read.

I would like to have someone knowledgeable look at my electrical system if anyone knows of someone her in Halifax. Unless you happen to be in town Paul.
Thank you!

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Thank you Don. Inflation won’t apply to sailboats if I get elected leader of Canada! Balmar Smart Gauge (square design and doesn’t require a shunt) doesn’t have Bluetooth but the SG200 model (round design) has the ability to add it a dongle. The Balmar has the ability to provide voltage level only when hooked to a stating battery. Others like Victron don’t know the difference between a starting and a deep cycle. Not sure it’s the end of the wold or not. Any info on this would be appreciated.
Thank you, David

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I have a Balmar SG200. It does have a shunt and can monitor my house bank (AGM) and voltage on my Start battery. You need a separate shunt to fully monitor another bank but one gauge can handle multiple shunts. The best part about the SG200 is that it learns as it goes and monitors your battery’s state of health which it then takes into consideration when it gives you SOC.

That means that if you have used 30 Ah from a 100 Ah bank most monitors will tell you that you have 70% SOC regardless of the age or abuse of the bank. It only knows that you told it the bank was 100 Ah.
The SG200 knows what the bank’s capacity is now and factors that in. It may tell you after a few years that your SOH is 95% which means that when you use 30 Ah, you actually have only 68.4%.
This may not seem important but I really like the full “state of your battery” information that it supplies.

You can also see at any given time exactly how many amps are going into or coming out of your bank.

Paul M
NS30U #211, Sandpiper
Cowichan Bay, B.C.

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I spend my entire season on moorings. I have 200 watts of solar attached to the Bimini with a 30-amp MTTP controller. On a good day the panels can do about 6 amps with full sun for about 6 to 8 hours. Otherwise, it is about 3 amps

My house back is 3 group 31 deep cycle marine AGMs that are located under the Starboard side settee. The starter is 1 group 31 AGM dual purpose.

I have an ISOTHERM ASU COLD PLATE ASSEMBLY that draws about 3 amps when running.

The boat came with an OFF, 1, 2 and ALL battery switch

The two things I added that you should consider.

  1. Blue Sea ACR BatteryLink Automatic Charging Relay, 120A 12V/24VDC | West Marine. This keeps the starting battery separated but allows it to be charged.

  2. Blue Sea low voltage cut off. I put this on the Cold Plate circuit. It will automatically shutoff the frig if the house batteries are getting low. m-LVD Low Voltage Disconnect | West Marine.

Peter Farley

Knot in a Hurry u30 #328

Keyport NJ

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David,
Interstate lists a deep cycle wet cell group 24 as having 77 ah.

When you say there is no room in the box for bigger batteries are you referring to a plastic battery spill protection box or the actual area under the berth? The starboard quarter berth on the 26C is referred to as a wide single or a honeymoon double. By using AGM batteries I was able to do away with the spill box and could fit in two group 31 batteries in an L pattern. The brochure for the 30 classic also shows the starboard quarter berth to be a double so hopefully you have a bit more room than you think.

If space is a really issue you could consider going to a single group 31 Lithium for the house bank and a AGM group 24 for starting. I use an Optima group 24 for starting a 20 hp Beta and it has been preforming well for several years. I had it capacity tested last year and it puts out more than the rated cold cranking amps. The charging needs are very close to the same as those for a lithium battery. If the batteries are properly wired in the AGM will protect the alternator if the battery management system on the lithium shuts it off. A 100 ah lithium will reliably give you 80 ah when you are out cruising and simply relying on an alternator for charging. Lithium batteries are happy to stay in a state of partial charge and do not walk down in capacity like lead acid. A single group 31 lithium battery and a group 24 AGM will cost close to the same as 4 group 24 AGMs.

The Nautilus brand of battery chargers was/is sold by Canadian Tire. I could not find a 25 amp charger but they still list them. https://www.canadiantire.ca/en/pdp/motomaster-nautilus-15a-onboard-battery-charger-0111521p.html
I came across a discussion forum where one of the contributors said the Nautilus are made for C.T. by Schumacher. According to the individual Schumacher made good chargers. When I first got La Reina I used a Nautilus portable charger. It worked well for several years until the cooling fan gave up the ghost, after which the charger quickly burnt out. If you go with the same size of battery bank you currently (pun?) have you cold keep your existing charger.

Here is a link to Practical Sailor’s 2005 review of battery chargers. It is getting out of date however the article says it was updated in 2019.
https://www.practical-sailor.com/systems-propulsion/electrical/battery-chargers-newmar-earns-best-buy-status

Rod Collins from Marine How To likes the Victron chargers. He also seems to think the Sterling chargers are pretty good. I believe they are sold in Canada under the ProMariner name.

I have a Xantrex Lite Link battery monitor installed. It is okay but I think there are betters ones available that will provide more accurate and useful information. Paul Miller will give you better advice on the issue than I can. My brother has done a lot of investigating into battery monitors and decided to go with a Victron.

Mark Powers
I was typing this on an iPad and just before I hit send I lost the draft. This is the second run at it so I am not proof reading. Sorry for any mistakes.

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Hi Peter,
With the ACR do you mean the link would allow the starter to be charged by the house bank if needed? My understanding is when charging with alternator I can switch 1, 2 or both to charge either of the 3 options. With the shore power charger it would detect which bank needs more charging attention. And with the solar panel I wasn’t going to bother hooking it up to the starter battery because I would give it the most attention under power.
Let me know if I have this wrong.
Thank you
David

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For alternator charging of multiple banks consider an FET isolator. It serves basically the same function that the (originally installed I believe) diode isolators used to except with almost no loss of power.

https://youtu.be/kz-QaSqznVg

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Hi Mark,
The berth is the starboard wide “honeymoon” double. According to my wife the honeymoon is over because she ain’t squeezing in there with me!
I’ll check the height and if there is a spill box. I haven’t noticed one in the past. The 4 batteries are pretty snug in there and the closest to the centreline don’t have a half inch to spare in height.

The problem with going to lithium is the added arrangements needed for the alternator and a DC to DC charger etc. You mention above that you didn’t need any additions to the alternator? A 200Ah lithium at Renogy is $1380cdn taxes in and $650 for an AGM with starting power. Next time I buy a Nonsuch I’ll know what I want it to have without me having to do it all myself after the fact!

I did read the article on chargers and all made sense. Thank you Mark
David