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