House Batteries got hot

[BDofMSP]

Catalinajack,
Thanks for the advice. I love doing research and you have me some direction to start in. Very helpful.

Thanks!
BD

 

[catalinajack]

Art, yes, going below 50% does shorten life for the reasons stated. No manufacturer that I know says otherwise. However, occasionally, or even somewhat occasionally, doing so will not shorten life in any amount that I would care about. Sure, consistently going to 20% or 30% will significantly shorten their life. But, take a look at East Penn's or Trojan's cycle life charts. You will find that going to 20% consistently, an extreme case, reduces cycle life by about 50%. So, if one is willing to accept replacing batteries every four years rather than eight years, well, that is just another boaters choice. Going to 40%, sir, even more than occasionally, is simply not significant overall. Let's say that for every cycle down to 40% reduces life by one cycle. Say that I go to 40% five times per season. Over eight years that would be 40 cycles less use. Not a big deal. So, here's a question for you? How about NEVER going below 80%? Your batteries would last for twice as many cycles. My point is, that the 50% level is just another benchmark. It is not a failsafe. As for safety, I don't see a problem except if a battery shorts out but, then, your 50% batteries are subject to shorting out at the end of their life in the same way.

Safety is as safety does! Each to their own!! Ya just never know!!! and all the other soliloquies ...

In my experience: A deep cell wet, LA batt, when its charge is brought below 50%, faster sends and piles up debris on the bottom of batt container [even when fluid level is full]. Eventually that buildup can create a short between cells. Therefore raising batt temp and reducing batt usefulness... such as happened in one of the posts above.

 

[catalinajack]

I went to the marinehowto website and reread some of the articles. Lots of good info there. The article you could read first is "Automotive Alternators vs. Deep Cycle Batteries". Next, if you want to convert to external regulation, read "External Regulation Conversion". However, those automotive alternators you have may not be strong enough to charge a large bank of AGMs. There is also an article on "How Fast Can an AGM Be Charged?". Lots of bathroom reading in your future. Good luck.

Catalinajack,
Thanks for the advice. I love doing research and you have me some direction to start in. Very helpful.

Thanks!
BD

 

[OldDan1943]

If you check, as I did, the expected life of a 4D AGM battery is about 4 years.

A quote from Lifeline battery's site:

"How can you make sure that your battery lasts as long as possible?
Make sure that you always discharge your battery at least 20% before recharging it, and do not let the charge go below 50%. Also, it’s very important to always avoid full cycle charging (e.g. charging from zero to 100%)."

Else where on their site, the indicate about 4 years.
https://lifelinebatteries.com/2020/05/how-long-do-agm-batteries-last/

LifePO4 indicates about 6 years. LFP batteries

Someone smarter than me can do the math and determine if the cost/amp/year of the LifePO4 is worth the extra cost.

I use my batteries as "just another power source." and let the Alt, gen, solar panels take care of the standard AGM batteries.
I do have a stand alone 40amp charger and a factory installed standard alternator on the Cummins 380 engine. I think it is a 120amp alt.

 

[Art]

Art, yes, going below 50% does shorten life for the reasons stated. No manufacturer that I know says otherwise. However, occasionally, or even somewhat occasionally, doing so will not shorten life in any amount that I would care about. Sure, consistently going to 20% or 30% will significantly shorten their life. But, take a look at East Penn's or Trojan's cycle life charts. You will find that going to 20% consistently, an extreme case, reduces cycle life by about 50%. So, if one is willing to accept replacing batteries every four years rather than eight years, well, that is just another boaters choice. Going to 40%, sir, even more than occasionally, is simply not significant overall. Let's say that for every cycle down to 40% reduces life by one cycle. Say that I go to 40% five times per season. Over eight years that would be 40 cycles less use. Not a big deal. So, here's a question for you? How about NEVER going below 80%? Your batteries would last for twice as many cycles. My point is, that the 50% level is just another benchmark. It is not a failsafe. As for safety, I don't see a problem except if a battery shorts out but, then, your 50% batteries are subject to shorting out at the end of their life in the same way.

Regarding wet cell LA batts: You are correct in all you say... So am I

As an adjunct: I consistently use East Penn deep cycle batts. Four Group 31 East Penn deep cell, LA batts are my house bank. They also are starters for my twin screw engines [i.e. two birds with one stone]. Last I needed to replace all four was a ten year span I purchase all my batts [marine and otherwise] at "Batteries + Bulbs" https://www.batteriesplus.com/produ...ne-and-boat/deep-cycle/bci-group-31m/sli31mdc They give good service and reasonable cost. Different LA wet batts they carry, to meet different needs, may carry different "tag" names... however, East Penn is the mfg.

 

[catalinajack]

Art, take a look at Rod Collins' marinehowto website. You will learn that Group 31 flooded lead acid batteries are not true deep cycle batteries despite what any manufacturer says. By the way, I did not say that what you aver was incorrect in any manner. I just don't angst over the 50% "rule" for reasons previously stated.

Regarding wet cell LA batts: You are correct in all you say... So am I

As an adjunct: I consistently use East Penn deep cycle batts. Four Group 31 East Penn deep cell, LA batts are my house bank. They also are starters for my twin screw engines [i.e. two birds with one stone]. Last I needed to replace all four was a ten year span I purchase all my batts [marine and otherwise] at "Batteries + Bulbs" https://www.batteriesplus.com/produ...ne-and-boat/deep-cycle/bci-group-31m/sli31mdc They give good service and reasonable cost. Different LA wet batts they carry, to meet different needs, may carry different "tag" names... however, East Penn is the mfg.

 

[TBill36]

This is all good stuff and I thought I had a pretty good set up for my needs and then the event that started this thread. I've read everything I can over the years on 12 volt systems - probably one of the more complicated things on a boat - especially since we're only talking about 2 wires - a plus and minus. I've cooked plenty of alternators and had very short battery lives throughout the years because of an unbalanced system. Started out with a ferrous transformer top brand charger that slowly cooked every battery I connected to it. Thought I was pretty well set up once and cooked a 90 amp alternator (internally regulated) because I drew down the batteries some one night and then I also turned on my 12v watermaker in the morning when I ran the engines. It's also the demands you put on your system that can make or break it. This event is the first that I've learned that a shorted battery is a potential for disaster . Has me thinking of going back to a single 8D as it would have less potential to produce the energy to keep heating up if a cell shorts out as the grouped together 31s did.

 

[Art]

Art, take a look at Rod Collins' marinehowto website. You will learn that Group 31 flooded lead acid batteries are not true deep cycle batteries despite what any manufacturer says. By the way, I did not say that what you aver was incorrect in any manner. I just don't angst over the 50% "rule" for reasons previously stated.

Jack - Here's a quote from Rod Collin's Marine How To website batt section:

"As I mentioned above Group 24, 27, 29, 30, 31, & most 4D & 8D flooded batteries are simply not a deep cycle product when compared to a battery such as a golf car battery, sweeper/scrubber battery or any other industrial application deep cycle batteries. GC2 6V batteries usually cost less than 12V batteries on a per ampere hour basis and also usually yield double the lab cycle life rating or more..

"...when compared to..." is the operative term.

IMO - Rod's Meaning: If you want to purchase considerably more expensive and well more heavy weight, commercial duty "Deep Cell" batts for your boat... then have at it... and you will get more robust Deep Cycle batts that last longer.

However, IMO and experienced knowledge, if you want to have relatively light weight and not too large a size for ease of handling/storage on your boat then what Rod Collins feels, i.e. "Group 24, 27, 29, 30, 31, & most 4D & 8D flooded batteries are simply not a deep cycle product" "... when compared to a battery such as a golf car battery, sweeper/scrubber battery or any other industrial application deep cycle batteries." Then Have At it!

In closing I'll give you my cost breakdown for 10 years of Group 31 LA East Penn deep cycle batt service in our boat. Cost of four [4] batts [discounts included] - $ 440 + tax. Cost of installation $0... as I could handle them myself. $$ Equivalents: Per year $44. Per month $3.67. Per week $0.88. Per day $0.13. Per hour $0.005 - LOL!!

I'm not for a minute saying that paying more for, installing bigger heavier and making long term use of industrial application [commercial-use] Deep Cycle batteries is not a good thing nor a bad thing... cause it is for sure a fine thing! What I am simply saying is that the less expensive, lower weight, less rugged construction wet cell LA Group 32 batts... called "Deep Cycle" by manufacturers and retail sales outfits - Work Well For Me!!

 

[bayview]

TBill:

IMO you understand what you are doing and the results look good to me. I would just go boating and recheck the SGs after a bit of normal use.

 

[Bacchus]

"Real" Battery Life Analysis

Art, yes, going below 50% does shorten life for the reasons stated.
No manufacturer that I know says otherwise.
However, occasionally, or even somewhat occasionally, doing so will not shorten life in any amount that I would care about. Sure, consistently going to 20% or 30% will significantly shorten their life.
But, take a look at East Penn's or Trojan's cycle life charts. You will find that going to 20% consistently, an extreme case, reduces cycle life by about 50%. So, if one is willing to accept replacing batteries every four years rather than eight years, well, that is just another boaters choice. Going to 40%, sir, even more than occasionally, is simply not significant overall. Let's say that for every cycle down to 40% reduces life by one cycle. Say that I go to 40% five times per season. Over eight years that would be 40 cycles less use. Not a big deal. So, here's a question for you? How about NEVER going below 80%? Your batteries would last for twice as many cycles. My point is, that the 50% level is just another benchmark. It is not a failsafe. As for safety, I don't see a problem except if a battery shorts out but, then, your 50% batteries are subject to shorting out at the end of their life in the same way.

I absolutely agree if you measure battery life in cycles - # cycles IMO is a very poor measure of batty life. What you fail to take into account if in the above statements is the reality that if you go to a larger DOD you are getting more AH's delivered - or the inverse - in order to reduce DOD you have to limit AH's used. To cut the DOD in half with a given AH demand you need to either recharge twice as often or install twice the batty bank. Recharging twice as often doubles the # cycles and the Life in years is the same. Doubling the bank size doubles the $ so the real cost is identical if cost is a consideration at all.

Measuring batty life in cycles is like measuring auto life in # trips - and if you limit trips to a max 100 miles your car will "last twice as long" as 200 mile trips - Not true - you only get more shorter trips.

Think of battys as a power source and you will find you can basically get a nearly fixed amount of power (AHs) from it. You can remove a little bit and refill it often or remove more and refill it less often or you can parallel 2 (at 2X the $ investment) to have it provide 2X the AH AND keep DOD the same.

ALL batty mfg I have seen (and open to any all instances anyone can provide) show similar lifecycle charts and if you do the calculations the oft quoted dramatic reduction in "life" is only a reflection of my statements above and the only way to get more AHs to use is more frequent recharge (which adds more cycles and does not really improve the available power (AHs) by more than 5% not the 50% often quoted).

Ill attach both the Lifeline and US BAtty charts and you will see they are very similar. I will also attach a file that does the calculations I mentioned above for several DOD points demonstrating the REAL life (AH delivered) is nearly constant. And when / if you compare situations over the complete life of a batty and include the cost you will find there is no free lunch.
IMO this isn't magic it's the nature of batteries - they are an energy source and within a relatively small bank are able to deliver a fixed amount of energy - unless we as owners "kill" them prematurely with poor handling... but using more than 50% DOD is not one of those things that "kill" battys.

I know I won't change the minds of many folks quoting the "50% DOD Rule"- just trying to present a different way of looking at the real economics.

I have also included quotes from Trojan citing 80% DOD as a reasonable limit and makes no mention of the need to limit DOD to 50%

 

[catalinajack]

I absolutely agree if you measure battery life in cycles - # cycles IMO is a very poor measure of batty life. What you fail to take into account if in the above statements is the reality that if you go to a larger DOD you are getting more AH's delivered - or the inverse - in order to reduce DOD you have to limit AH's used. To cut the DOD in half with a given AH demand you need to either recharge twice as often or install twice the batty bank. Recharging twice as often doubles the # cycles and the Life in years is the same. Doubling the bank size doubles the $ so the real cost is identical if cost is a consideration at all.

Measuring batty life in cycles is like measuring auto life in # trips - and if you limit trips to a max 100 miles your car will "last twice as long" as 200 mile trips - Not true - you only get more shorter trips.

Think of battys as a power source and you will find you can basically get a nearly fixed amount of power (AHs) from it. You can remove a little bit and refill it often or remove more and refill it less often or you can parallel 2 (at 2X the $ investment) to have it provide 2X the AH AND keep DOD the same.

ALL batty mfg I have seen (and open to any all instances anyone can provide) show similar lifecycle charts and if you do the calculations the oft quoted dramatic reduction in "life" is only a reflection of my statements above and the only way to get more AHs to use is more frequent recharge (which adds more cycles and does not really improve the available power (AHs) by more than 5% not the 50% often quoted).

Ill attach both the Lifeline and US BAtty charts and you will see they are very similar. I will also attach a file that does the calculations I mentioned above for several DOD points demonstrating the REAL life (AH delivered) is nearly constant. And when / if you compare situations over the complete life of a batty and include the cost you will find there is no free lunch.
IMO this isn't magic it's the nature of batteries - they are an energy source and within a relatively small bank are able to deliver a fixed amount of energy - unless we as owners "kill" them prematurely with poor handling... but using more than 50% DOD is not one of those things that "kill" battys.

I know I won't change the minds of many folks quoting the "50% DOD Rule"- just trying to present a different way of looking at the real economics.

I have also included quotes from Trojan citing 80% DOD as a reasonable limit and makes no mention of the need to limit DOD to 50%

Thank you, Bacchus, for explaining in a more technically accurate manner what I was trying to get at in a more inexpert way. The bottom line is the "50% rule" is a rule with no basis in fact. There is a finite amount of energy to be derived from a battery. Battery life is wholly dependent on how much they are used whether depleted to 80% or 30% or anywhere in between. Boats that spend more time at the dock compared to others that are away from shore power, sure, the batteries last a long time. I get a chuckle from guys who say this and that and my batteries lasted 8, 10, 12 years. Means nothing. Use them, lose them. Dock queens, well, of course their batteries last a long time. So, I say again to the rookies, do not be afraid to use your batteries but recognize that the bank account is not bottomless.

 

[Bacchus]

You've got it!
All above within reason of course...
I wouldn't recommend going beyond 80% DOD on a regular basis. Once or twice not instant death.
Battys dont like to sit depleted for long periods, etc.
They like to be fully charged frequently- like at least each week. Fully charge takes longer than many estimate or believe... like 12-14 hrs in many cases.
I laugh when folks say they started up and ran for 30 min to charge battys, etc, etc

Lots of knowledgeable folks on here but read a lot and figure out who the real deal folks are. OK to consider other opinions but worth confirming.

The only other comment I'll make is its important to have foljs specify if talking about Flooded, AGM, Gel or Li. ( I know little about Gel and less about Li).
If I believe the quoted life EXPECTANCY my thinking is I won't be around long enough to ever break even so have seriously considered the investment as an viable option for me.

 

[BruceK]

Hard to see that discharging to 49% instead of 50% somehow attracts the fires of hell and eternal damnation, for the battery. Surely it`s just a number. As always, rely on commonsense.

 

[Art]

Hard to see that discharging to 49% instead of 50% somehow attracts the fires of hell and eternal damnation, for the battery. Surely it`s just a number. As always, rely on commonsense.

Basically it comes down to power in / power out... with a couple of battery life-term and charge ability encumbrances; depending on how deep the discharge is allowed to become.

So... for wet cell, LA, deep cell batts why not recharge at 50% discharge rather than let's say dropping down to 70 or 80% discharge?

Encumbrances - a couple of relatively minor things:

1. Recharging at 50% is easier on the battery cells and does somewhat extend batt life, as compared to recharging at a further % discharge - especially all the way down to 80% discharge .

2. There is always a percentage of power-loss between the charger [of any type] regarding the level of charge actually being absorbed into the battery. And, although I may be incorrect, I recall reading that the initial incoming charge to a battery, during its considerable level of discharge, has [at least at first] an added percent of a charger's power-loss per charge energy the batt absorbs.

Neither 1. or 2. amount to a big difference for using LA deep cell batts... but... in my opinion... every little bit of efficiency helps!