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Old 05-15-2016, 09:43 PM   #11
Senior Member
Join Date: Mar 2014
Posts: 634
Originally Posted by northstar1960 View Post
keeping batteries on a maintainer and always fully charged will promote sulfation . drawing a battery down to 75% or more and then charging is the way to go . take a 100 amp hr battery down to 50 % and then slow charge 3 amp or less will give you a good full charge in a day
That is NOT what is published on any lead acid battery manufacturer or expert web site.

Sulfation occurs during discharge, not during charging. Charging drives the sulfur back into the water-sulfuric acid solution from the lead sulfate molecules formed on the plates during discharge. During deep discharge or over time, some of the lead sulfate molecules become crystals, which are much harder to break apart than normal soft lead sulfate. If the battery is kept fully charged or close to it, the incidence of crystals becomes much less.

Thus, the life of a deep cycle lead acid battery is driven in part by the number of discharge cycles. The deeper the discharge before recharging, the smaller the number of discharge cycles before the battery is toast. The 50% maximum draw down is based on a trade-off between usable battery capacity and number of discharge cycles before the battery is toast.

If you limit discharges to 75% SOC (state of charge), you have more discharge cycles available to you from the battery. If you limit discharges to 90% SOC, you have even more discharge cycles. This is what the charts from battery manufacturers show.

For optimum battery life, recharge as soon as possible after discharge. Limit your discharges to 50% SOC or greater. And most important, keep the water level above the top of the lead plates.

Whether maintaining a battery with a low voltage (13.2V or so) is better than letting the battery sit disconnected for a month and then recharging to 100% is still an open question. There are proponents in either direction. Personally, I am not persuaded that either choice makes the difference in battery life that deliberately discharging a battery to 50% or letting the water level get low will.

In the end, I'd just like to get at least 3-4 years out of my golf cart batteries. More would be nice, but the difference between the 7th and 8th year of service is not that important to me. I refuse to spend my camping life playing battery monitor.

Fred W
2014 Rockwood A122 A-frame with 2 Interstate GC2 6V 232AH batteries from Costco ($150 for both in 2015)

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