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keith7wa avatar image
keith7wa asked

AGM Telecom Batteries as Boat House Bank? BAT412181164

I am considering replacing my aging yacht house bank batteries (10 Northstar Telecom-style batteries 12v 217AH) with 12 Victron AGM 12v 200AH telecom-style batteries. These would be wired in series/parallel to create a single 1,200AH 24v bank to run house loads on the boat.

I want to stick with this form factor so I can reuse all the connector cables as well as the custom shelving and bracketing that exists on board—modified slightly to accommodate 12 instead of 10 batteries. My plan is to use these to a typical DoD of about 35% to 45%.

I am fairly well versed in Lithium but have decided to remain on the AGM chemistry for now for various reasons.

My questions are:
- Does anyone here have experience with a deployment of these batteries in a similar environment? ie: As a house bank on a boat or RV.
- Will these function largely the same as other Victron deep-cycle AGM batteries that come in more traditional form factors such as 4D and 8D sizes?
- Are there any other special considerations I should be aware of with these batteries?
- Lastly...why are these so much cheaper than the similar offering(s) from brands like Odyssey?

Thanks in advance for any guidance!

batteryAGM Batteryyacht
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3 Answers
JohnC avatar image
JohnC answered ·

Hi @Keith7WA

I have no experience with these particular batteries. But they're Pb's, and I wouldn't consider running 6x parallel strings of them. They'll suffer imbalance, particularly as they age, and may fail early.

You won't find anywhere official where Victron recommend more than 3x parallel strings of pbs. And even then I reckon that's stretching it..

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christern avatar image christern commented ·
Just a personal comment on what I found out by asking some highly educated persons in chemistry and battery management. Here is what I have been told and what I fully understand.

AGMs (as well as other pb-batteries) have an increased internal resistance the more charged they get and by that they will get very balanced by themselves when charging them to more than i.e. 80% SOC.

Just think of the extended time it takes to get those batteries charged from 80-100% SOC. During this time the batteries with the lowest SOC will catch up to the others as their internal resistance is lower than those with a higher SOC.

By this I cannot see any logics in recommending to keep batteries within 3x parallel.

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kevgermany avatar image kevgermany ♦♦ christern commented ·
There's armchair expert theory and there are empirical observations.

I'll just say that my 4 batteries in 2 strings for 24V always go out of balance. And do not self balance to the extent that a dedicated balancer pulls them back. Despite a very heavily tuned and carefully installed setup with equal length cables etc.


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christern avatar image christern kevgermany ♦♦ commented ·
Thanks for your comment and sad to hear that your batteries always goes out of balance. That is however not my experience on my installation (boat w 6 x 95 Ah AGMs in house-bank). They have kept well balanced over the 14 years I have had this set-up. First set of batteries were kept for 10 years and still at the end they were well balanced (continously checked and also checked at removal). They continued, and still do, serving a small cottage on a remote island without any electricity and are powered by a small solarpanel. (However I think they are not sufficienty maintained by the current owner and may have very little capacity left now.)

So, I would say that in my case "empirical observations" supports theory, but this can naturally vary between individual batteries/cells and types of batteries.

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JohnC avatar image JohnC ♦ christern commented ·
@ChristerN

Pb batts are less efficient absorbing charge at high SOC, that's well known. That lost efficiency expresses as heat. And a hotter battery loses resistance, accepts more current, then gets even hotter - thermal runaway! Might be the best battery too that suffers this the most. And dies first.

I inherited a 6x parallel 12V system on my own boat. It was a nightmare. I changed it out for a single string 48V system with the same type of batts. It now performs better with 2/3 the number of batts. And they last way longer.

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christern avatar image christern JohnC ♦ commented ·

Thanks for your comment. I have never noticed any extended heat in any of my batteries however I must admit that I have not checked temperature of the batteries continously. None of them have however showed any indication of a thermal runaway.

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pwfarnell avatar image
pwfarnell answered ·

I have the 115Ah Victron telecom batteries in my boat on the UK inland waters, 12V system though. 3 years old now, used 5 months of the year but typically only discharged to 75-80% SOC. The rest of the year they are kept on storage by the solar or Multiplus. I track their performance, voltage vs SOC on the Cerbo and there has been little deterioration over 3 years so far, still showing a similar voltage at 80% SOC as new, but then they are seeing an easy life.

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keith7wa avatar image
keith7wa answered ·

Thanks all for the great information. It's common practice in the boating world to build fairly large house banks out of many AGM batteries and similar to @pwfarnell's experience, most of us have great luck with this and long service life.

But I will give good consideration to keeping my bank balanced as much as possible.

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