Sizing battery for minimum depth of discharge. Does it matter?

larcal · October 2021

Granted that deep cycle kept in float without monthly recycling to 50% ruins capacity because lead dioxide builds up on positive plates. However, the minimum DOD below float that one can safely dance around (usually 10%) is rarely mentioned and never with any proof, data.

Rolls . for instance, apparently frequently verbally discusses need for exercise but does not even mention 10% in their bulletins etc, nor any other advice around this. At least their cycle charts end at 10%, which is a minimal clue, whereas other company's charts go right to zero. There are reports the Rolls techs actually say, (but don't write down) a figure of 20%

Amazing, how long has off grid energy been around?

So, basically requesting here that you all chime in if you have any experience or strong belief in this area. Will a cell last noticeably longer if sized small enough that your daily consumption will pull it below 10% daily?

Generally, it is supposed that when comparing two batteries identical in plate thickness the one with the higher amp hr capacity will get more cycles cause dod is shallower.

However, when if the larger cell is regularly discharged 7% while the smaller goes down 13% will the smaller last longer because it is over 10% even though it has fewer cycles due to lower ah capacity?

Emotionally,or whatever, one just wants to get the biggest battery one can afford and/or move. Moerrrrrrrrrrrrrrrrrrrr.....

Thanks for any insight.

mike95490 · October 2021

Thicker plates generally last longer

larcal · October 2021

Mike- i said I knew that and took that out of equation. This is about relevancy of supposed truth that lead oxide builds up on positive plates when dod is above 10 % and whether this should affect sizing of battery

Dave Angelini · October 2021

Given the same good maintenance, the larger cells will last longer, as long as both models are not taken below 50% too often. Very hard to prove however. Just experience from close to 500 offgrid applications.

Long posts often get the same amount of thought as shorter to the point posts. I know I do not have time to read it all and I suppose others also feel this way. Staying to the point may get better responses. Good Luck!

larcal · October 2021

Thanks Dave, good criticism and have heavily edited. does your belief hold in the example just gave, with two cells close to but on opposing sides of 10%?

Sizing battery for minimum depth of discharge. Does it matter?

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