Thor Forums

[blw2]

[QUOTE=Beau388;156515]

Originally Posted by blw2

re. that 50% rule of thumb....


from Trojan's user guide...
"Do not discharge your battery to more than 80% depth of discharge. This safety factor will eliminate the chance of over-discharging and damaging your battery"
(means that you should be able to take it down to 20% of the capacity (100-80=20) QUOTE]


The quote is correct but your inference is not. Discharging any lead acid battery beyond 50% of it rated capacity, VLRA, AGM, GEL or flooded, will shorten it life span. Drawing the battery down to below 20% of its rated capacity tends to kill it outright, just like letting the water level get below top of the plates kills a battery. How much will that extra 30% of discharge shorten battery life is debatable among battery manufactures, but it is significant (up to 1/3 in some batteries). After all; all lead/acid batteries use the same chemistry. Alloying the plates with antimony, selenium or calcium doesn't change the chemistry. The paste used is inert and only acts for a seed for the lead sulfate crystals and leads to a higher potential discharge rate without stratification.

maybe so...but everything has a finite number of cycles....and what good is a tool or a toy if it's not used to it's potential.

Regardless, I'm no battery engineering expert, but my gut logic tells me the switch from ok to shortened life is not a specific finite level...and it's not likely even linear.....also I'd guess it to be a very safe bet that a starting battery compared to a true deepcycle compared to a marine hybrid do not all three trip over to the same amount of relative "damage" at some magical 49.599%...or whatever the number....
but regardless, if 50% is good, why not set 51% as your floor....or 53%....or 75%? Wouldn't that be even better from the perspective of maximizing life?

It seems more or less generally accepted that the deeper they are discharged the shorter the life....and at any give discharge rate they have some finite number of cycles. Not arguing that of course, and I see your point...but I've gotta believe that if Trojan says it's ok to draw down to a 20% floor "without damage".....and keep in mind they would apply a factor of safety to a spec....then it seems it would be ok for me to add another factor of safety to the number and set let's say ballpark 35% as an acceptable floor...well below the 50% rule of thumb...so certainly 45% would be good, right?

Anyway, I guess my overall thought is to ask what is my goal in it? Is the end game to get my money's worth out of the battery, or is it to never have to buy a replacement the rest of my life but never use the thing?