How to test working capacity of battery: not technical

[profdant139]

(If you are a highly sophisticated technical battery expert, I advise you to stop reading. This post is designed for people like me, who are not experts.)

I have two group 31 12V marine deep cycle batteries, which supposedly have a total capacity of 110 amp hours. In the real world, that means that they have a theoretical working capacity of only 55 amp hours, since I am told that it is not good to draw the battery down below a 50 percent state of charge. When the measured voltage gets down to 12.1, that's a 50 percent state of charge.

So I wanted to see if I really have 55 amp hours available. That information is useful for a couple of different reasons: first, if I do have that much power available, that tells me that my usual battery maintenance routines are adequate. If I don't, I have to do something different. And this reading will provide me with a baseline, so that I can tell when the batteries are starting to get old. Finally, if there is a material difference between my two batteries, that would be very interesting (and disturbing), since they were purchased at exactly the same time and have been used in exactly the same way.

(As you'll see below, the results were not what I was expecting. Hint: this story turns out well.)

My overall plan was to hook up a lamp and then to see how long it took to draw the battery down to roughly 12.1.

I started with a fully charged battery (which reads 12.9 V when it comes off the charger) and then let it rest for a day, so that the initial reading was 12.7 volts.

I then hooked up a 60 watt incandescent bulb, plugged into a small inverter, which was plugged into a "cigarette lighter socket" adapter, which has alligator clips that go to the battery terminals. (If you don't have one of those adapters, they are really handy when you want to hook a 12 V appliance directly to a battery.) I then used my multimeter to find out how much current the bulb and the inverter were drawing, which was 6.1 amps.

(If you already know how to measure the amount of current that a device is using, skip this paragraph. Personally, I can never remember how to do this, so I have to reinvent the wheel every time.) Put the red (positive) multimeter plug into the "10 amp" socket on the front of the multimeter. Turn the multimeter on to the 10 amp setting. It should read "zero." With the lamp still plugged into the adapter, unhook the cigarette lighter adapter's black alligator clip from the negative terminal of the battery. Touch the multimeter's black lead to the negative terminal. Touch the multimeter's red lead to the unhooked black alligator clip on the cigarette lighter adapter. The meter will display the amperage.

Anyway, I left the light on for two hours, thus consuming 12.2 amp hours. I unplugged the light and let the battery rest before taking a reading. I was told that it had to rest for two hours to settle down. But with careful measurement, I discovered that after a half hour of rest, the voltage had plateaued and did not continue to change. (Maybe that's not true of all batteries, but it certainly was true of mine.) So for the rest of the experiment, I let the light run for two hours, followed by a half hour of rest, at which point I measured the voltage and then plugged the light in again.

Here is a table of the results:

Run-time Voltage

2 hr 12.6

4hr 12.5

6 hr 12.4

8 hr 12.3

10 hr 12.2

So this means that after ten hours of actual run-time (consuming 61 amp hours), the battery got down to 12.2 volts, i.e., with 60 percent of capacity still remaining. It looks like I could have gone two more hours to get to 12.1, for a total working capacity of 67 amp hours.

That is a lot better than the 55 amp hours of working capacity than I was expecting!

I did this experiment twice, once with each battery, and got exactly the same results. This tells me that this wasn't a fluke.

I am not sure how it is possible that my batteries are outperforming their rated capacity, but I'm not complaining. This won't change my consumption patterns when we are camping – we are very careful about electricity. But this is encouraging news, and it gives me a baseline for subsequent comparisons.

[westend]

I'll add my bit about "pulse charging". Years back, when working at a golf course where many batteries were maintained, both in equipment and in golf carts, we became the target for a company selling a discrete pulse charging device. This gentlemen was from Canada and professed to be a patent holder of this device. He had paper work of white papers describing the device and it's effects on different batteries and uses. He had studies of fleet maintained batteries in different use settings and the effect of his device on the longevity of these batteries. It all looked very good and the statements regarding an increase in longevity of 33% over other batteries not using the device was a serious lure to bite on purchasing his devices for maintenance.

At that time, the cart maintenance had been addressed and a new multi-battery power supply had been installed at many thousands of $$$. The clubhouse people had finally figured out that 16 yr old kids (cart boys) did not have the best interest of the Golf Club in mind.
The rest of our running gear was maintained throughout the year by staff that meticulously repaired and maintained the equipment. Batteries were tested prior to their lay-over in Winter and the short period of non-use had little effect on those batteries.
Hence, we did not purchase the pulse chargers. I often thought about the claims of these gentlemen and I came to the conclusion that the overall 33% longevity claim was caused by the constant power floating the batteries and not from some spike in milliamps and low voltage.

Mex has done the research and others I've had contact with regarding "pulse charging" agree, it does nothing for battery longevity but since it is paired with battery charging, the end user has benefit.
Pulsing the DC input probably has no ill effect except for possibly interrupting the constant charge, as some pulse chargers do. A pulse charger that boosts milliamperage in parallel with the constant power, will have little effect, IMO, on sulfation or battery health.

Edit: I agree with landyacht 100%. If a user has a battery of suspected capacity loss feed the sucker with a lot of juice. An AGM with bad symptoms can be treated alike, feed it the juice.

[landyacht318]

While I know that on many NON rv related forums and even by a portion on them, the trickle charge to full mindset is always viewed as best for recovering a battery, I am not in that camp at all.

If the battery is sulfated/ capacity compromised with somewhat hardened sulfate, and discharged, I feel that high amp rates will heat the plates and perhaps allow the sulfate to be redissolved back into the electrolyte.

I am of the mindset that one does not force a marathon runner or sprinter to breathe through a cocktail straw, but give them a row of macdonalds straws to suck as much as they can.

My experience with Desulfating pulse chargers, limited as it might be, and and marketing gimmicks in general, is that it is just another way of separating consumer from their money. And somehow making them feel good about it. All this seems to require is marketing material with lots of colors, outrageous claims, and blinking lights, preferably green.

Helps too if the plastic casing is sexy.

[MrWizard]

There was a time when I believed in the high current 'reconditioning'
Done by some of the homebrew devices used by off grid solar users

I don't think it is the pulse frequency that does anything
I think it is the high current pulse that does this
"High amps" not milliamps

It is away to shock? Inject high amps without overheating the plates and electrolyte

Pwm solar is just a 'switching power supply' a way to control the voltage
Like cell phone chargers and RV converters

[BFL13]

The 24 hour pulse "Recondition" session on a Vector charger does not raise battery voltage. So that is not "charging."

It is meant to be a way to desulfate. I have used this and am not sure it works. I do see that after a session of Recondition, you can get the battery to a slightly higher "full" than before, so I have used alternating Recondition sessions and high voltage charging sessions to "recover" batts when they got stuck at a "full" that was too low. (Back when I had those 27s that were so difficult to recover. Don't need to do that with 6s) It may be that just taking a day off between high voltage sessions would work the same, but I never tested for that.

Meanwhile, there is something called "pulse charging" which I suppose does raise battery voltage. I guess this would be like when an MPPT solar controller goes into Absorption and uses PWM. That is charging with rising battery voltage.

[landyacht318]

My buddy has a batteryminder 12248, and I would borrow it when I was noticing capacity loss.

This was back in Analog TV days and it would add some diagonal lines to the TV, which would move from the left to the right, and then stop and then go right to left. Turn off charger, no more diagonal lines. Other chargers the diagonal lines were almost always the same

I would leave it on the battery for 10 days, and then after one more discharge, I'd decide it was time for new batteries.

It always seemed to revert to the Gel setting after a period of time.

Worked oK as a converter when there were minor DC loads.

But 8 amps ain't jack.

[MEXICOWANDERER]

Maybe sometimes it could work is hardly a defining statement. Stanley Pons, endured the consequences of assumptive rationalization - he was staked to a. Ant hill. It is permitted an ethical for an adult to assume whatever belief they wish as long as it does not harm others. The minute a "sales job" comes into play is when it raises my eyebrows.

Pork The Other White Meat

[BFL13]

The UPG tech who likes pulse charging for AGMs, said it did, " 14.8, stop, 14.8, stop, 14.8, stop, 14.8----" as its way of pulsing.

I have no clue if that is what all pulse chargers do, or if that is what Mex is talking about.

One story a few years back was that the pulse was at a particular frequency that shattered the crystals. Not a clue!

Back then too, a lab test report linked in a thread on here, said it worked sometimes but not always, and that it was inconclusive whether you could count on it.

[pnichols]

profdant139 wrote:
Mex and I differ on the meaning of boondocking. When I spend about 60 days a year in remote country, that is boondocking to me. If I need to spend a year at a time, that is not boondocking. That is survival off the grid. What I do is a hobby, a vacation. Off grid survival is a business. If my life depended on the life of my batteries, I would be as scientific as Mex is.

And Fubeca, I am quite sure that if the BatteryMinder Plus were a hoax, a trial lawyer would have been contacted by a tech-savvy client and would have brought suit. No one has done so. Absence of evidence is not always evidence of absence, but in this case it just might be.

Excellent comments! I agree on your definition of "boondocking" ... except for any particular length of time being required. We sometimes drycamp in remote country for only 1-2 days. I call that hit-and-run boondocking. However, our "remote country" is usually desert - not the real stuff that you camp in.

Regarding BatteryMINDer Plus battery maintainers:

I've used the same one for years to maintain our motorhome's main engine starting battery. I'm only recently on my 3rd starting battery in nearly 11 years of owning our rig. I recently picked up another one to maintain the small AGM batteries in my garden sprayer and backup residence generator.

By the way, I've watched what a BatteryMINDer's "pulsing" is all about when it's maintaining a battery. It's not outputting medium-to-high frequency square wave pulses as might be implied or as some might think - which indeed might be fluvy-dust technology - as a storage battery's electro-chemistry can't respond to high speed voltage or current changes. What the BatteryMINDer is doing - at least according to my digital voltmeter - is slowly varying it's voltage output up and down. The rate of change is slow enough for it to perhaps have some affect on a battery's electro-chemistry. It's my guess that some beneficial affects from this behavior may be what BatteryMINDer marketing may be referring to. :h

[westend]

Mex,
Sometimes the failed experiments can bring good results. Your experience may not qualify as "good results" for you but at least you can educate the unlearned on pulse charging and what it doesn't or does do. That right there is a good result.
Thanks for posting about that.

[profdant139]

I don't go anywhere without my Phillips. I am old enough to remember the days when most screws were slot head -- my father let me "work" in the garage with him back in the mid-1950s. I miss some things about the old days, but I do not miss slot head screws. 😉

[NinerBikes]

profdant139 wrote:
Niner, thanks for that tip on using the panel to equalize -- I will give it a try after we get home from our next trip (which is coming up next week, depending on the weather).

If you have a philips screwdriver on you, you can do it on your camping trip, for a day, last day of the trip, no need to wait.

[profdant139]

Niner, thanks for that tip on using the panel to equalize -- I will give it a try after we get home from our next trip (which is coming up next week, depending on the weather).

[MEXICOWANDERER]

Interested battery OEMs paid my overhead expenses for pulse charging analysis. The bonded contract agreement was for me to patent my technology then give them exclusivity with regards to licensing. I discharged batteries at a 10 ampere rate GC220s also furnished by them. Total discharge. Rest discharged for 120 hours then recharge constant voltage acceptance for 10 hours. Repeat cycle. After 20 - 50 cycles the batteries would be significantly sulfated. Divide into three groups: 1) Immediate plate disassembly 2) Conventional BCI equalization doctrine applied 3) Varying algorithims of pulse charging. With a 3 phase 20Kw 1-20KHz Westinghouse generator. 0-255 volts I could discipline DUTs as I pleased. This went on for almost four years intermittantly. Using a 10x loupe I cpuld find no significant evidence that any form or recipe of amplitude or frequency would affect latticed PBSO4 better than a regimented maintenance charging regimen. I did find significant evidence of plate boundary interface damage (meaning cured plate paste) softening and shedding of relevent active plate material. What affected latticed PBSO4 destroyed viable plate material. At the end of the exercise I was furnished an unnamed marketed device that proposed "pulsed desulfation technology" kWh transactions were monitored and recorded. I found no significant evidence that pulse charging reduced or removed accumulated PBSO4. A lot of time wasted. Dreams dashed. And 1800 dollars out of my pocket for patent research and initiation. I refused to pursue the issue which upset two companies. They forced me to sign packets of ninety-nine year non-disclosure contracts. So yes I am touchy about this subject. And this I'm afraid is the very last time I intend to broadly cover this. It was a major failure in my life. I can only be satisfied by the fact I treated it publically as an "impersonal exercise" and did not color the prospects. OK Enough...

[landyacht318]

I personally have no faith in the legal system to keep marketers/ purveyors of products from making ridiculous claims which might very well refute the laws of physics or any objective testing.


There is profit involved, grease the right palms and they can and will say anything to increase sales, profits, and then baby gets a new shiny diamond even if quality is destroyed and the product reputation starts faltering fast. When that occurs throw the marketing department a little more Baksheesh.

There is NO truth or Honor in advertising/ marketing. That ship sailed long ago, and the few that did not follow suit were pushed out.

Make enough glossy marketing and the modern consumer could apparently be persuaded to believe the pet rock is actually a functional good luck charm able to endow the owner with genital prowess.

Or in this case, magically restore shedded plate material and turn back time.