Is there a correct battery voltage chart?

I had two different AGMs, one an 8D and another was a 27. Both had similar charts for Voc vs SOC. A fairly wide band as seen here (scroll down and to the right)

http://www.wegosolar.com/products.php?product=SKR%252d125AGM-Stark-AGM-12V-Solar-Battery-Sealed-125A

It turned out with my AGMs, that 12.4v was about 50% as confirmed with Trimetric AH counter. They rested full (after the 0.5a/100AH target and a few days later) at 13.0V

So my AGMs were in the middle of that band on that graph, but I had to learn that using the Trimetric. No other way to tell.

My flooded 6s and 27s are more like the Trojan graph, also confirmed by Trimetric. So it was easy for me, just add 0.3 to the Flooded voltages to get the AGM voltages for estimating.

I found it took a couple of days for the surface charge to go away after a recharge so the Flooded batts were 12.7ish. You can knock the surface charge off in a hurry if you want, but then it is hard to know if you overdid it, so your resting voltage after that could be too low.

Just to follow up after getting the reply from Motobat batteries..There battery is closest to Nicks test than the others on the chart..They did have it tested by an independent place.I thought so but was not sure,this confirms some of those charts out there are not up to par with different batteries..

Your batteries are too low when the inverter quits at its (say--they vary) 11v alarm/shut off voltage as seen by the inverter (wire gauge and length involved there too).

EG, with our set-up I get a 0.9v drop with the inverter pulling 125 amps. (This could be improved, but no need to.)

So if the bank is at 12.7 (no solar charging happening) the inverter sees 11.8 at first, then drops to whatever as the load keeps running. Might get to 11.6 before the MW is done.

So to stay above 11, I need to have at least 12.1 going in. I have no problem with going down to 40% SOC if need be, and the lights and furnace will still work ok, but the inverter will alarm off with the bank that low.

I accept the fewer lifetime deep cycles so the bank needs to be replaced every five years instead of eight years, so that I can run the inverter how I like.

jaycocreek wrote:
I was watching 'lil Will Prowse and he said never take your battery below 12.2 volts..By the chart I had downloaded,that would be about 65% which doesn't sound right as 50% has always been the gold standard to to exceed for battery longevity..

So I wonder what chart he goes by or if it is off his solar charger or one of his other gadgets..

I still have not heard from my battery company but they are located in Florida and alot is going on there now...

The idea to never take a battery below a certain level is a misunderstanding of battery system design guidelines utilized by system designers. The guideline is that for the best trade off of battery life/economy/weight/size/charging time, you should size your battery/bank such that the average depth of discharge is no lower than 50%

This is widely misinterpreted to mean you should never discharge a battery below 50%. This is complete nonsense. It is spread widely by battery dealers, who are on average as misinformed about batteries as anyone could be.

If you look at a graph of battery cycle life vs. average depth of discharge, you’ll see that below about 20% DOD, the chart is linear all the way down. That means there is no magical tipping point at 50% or 65% or any other number after the 20% level. The deeper you discharge it, on average, the shorter the life, but 55% is only worse than 50% in the same way 50% is worse than 45%. If there was a point where sudden significant loss of capacity or life occurred, there would be a knee or change in slope at that point.

The only time you should worry about battery discharge levels is when you have limited charging availability or when you are buying new batteries. When buying batteries you should size them so your average DOD between charges is 50% or less.

They won't know because it remains an ambiguous question. Go ahead and give it your best shot. Then corroborate your best shot with a hydrometer. People have tried and failed using fuzzy logic algorithms.

Electro chemistry is 95% chemistry and 05% electricity.

I was watching 'lil Will Prowse and he said never take your battery below 12.2 volts..By the chart I had downloaded,that would be about 65% which doesn't sound right as 50% has always been the gold standard to to exceed for battery longevity..

So I wonder what chart he goes by or if it is off his solar charger or one of his other gadgets..

I still have not heard from my battery company but they are located in Florida and alot is going on there now...

This is the type of game that has to be played if you use derivatives to guess at the state of charge via voltage.

• Before a "reading" is taken no and I mean NO ZERO NONE battery draws can be present. Not even a CO detector
• A test load like a lamp should be enabled and a stable voltage must agree with what you have experienced doing this in the past
• Peukert enters the picture, with riding boots on
• The higher the draw, the greater the apparent error
• Where and when are your shutdown points?
• Unless your habits resemble those of a Trappist Monk, using dependable extremely light loads, control by voltage is fraught with expensive error
• At the expensive expense of your battery's health the only way to gain insight is through Trends & Tendencies
• Like learning how to prepare French cuisine
• Instead of screams of "This tastes like ****" you pay a 300% penalty in battery life
• If there are no red and blue lights flashing in your mirrors, you must not be speeding, right?

No thanks. Amp hour meters used to be expensive and more of a valid excuse. Not any more. Next, I expect to read about a miracle tire bat that resounds in the key of "G" when it encounters 80 lbs.

I just use the rule of thumb: don't ever let it hit 12v.

Voltage is a horribly inaccurate way of measuring battery capacity. That's why the charts are all over the place. Battery design, specific gravity, temperature, charging or discharging currents, and probably some other things come into play.
To really know what's in a battery you need a battery gauge. A battery gauge will have a shunt; if it has no shunt it's not a battery gauge. Tri-Meteric makes a nice one as do Victron, Magnum, and Outback.

Different manufacturers and different technologies have different voltages at varying states of charge. That is why the charts vary. The voltages also vary with temperature, and as noted, if you have recently drawn power from the battery the reading you get won’t be accurate.

Really not worth worrying too much about it.