Battery Self Discharge

[Gjac]

Would the rate at which a battery self discharges be a way of determining the health of a battery? I have (2) 7 year old Sam's Club GC batteries that have been sitting without charge(battery disconnect switch on) since Nov 4 2014. On Jan 10 2015 they read 12.48 V at 20 degrees F. I know a load test would be the normal test, but I am in Fla now and the MH is in Ct. So is there a direct correlation between the rate of self discharge and how many more years a battery would last assuming the same usage as the previous years?

[JamesJudasPries]

If you have left your inverter connected, even when switched off, that may contribute to a slow drain. I might be mistaken but I think the DC input's large capacitor is still in the circuit when the inverter is switched off, which may rob you of a few Amp hours over the weeks. I noticed this when I would connect my inverter with battery clamps and get a spark even with the unit switched off.

[MEXICOWANDERER]

Low temperatures make me wanna do nothing too. My top charge is a cup of French Roast and that's no guarantee I'll be worth two cents after I drnk it. I empathize with the battery. BTW cold battery acid is the reason for cold weather battery blues. Chemical reactions are frequently dependant on thermal value.

[jrnymn7]

O.K., mystery solved (I think).

Dec 21st, Temps a little below freezing (IIRC), OCV was 12.74v. I was heading out of town for two weeks shut down work, so I did a quick top charge at the Peaks 4a setting, but only for about an hour. Charge ended at 4a @ 15.03v.

Some fairly cold days in between.

Two weeks later, Jan 4th, Temps at about 32F, OCV was 12.71v. Top charged at Peaks 20a setting until 7.2a @ 15.63v.

Some very cold days in between.

Two weeks later, Jan. 18th, Temps at about 40F, OCV was 12.73v. Top charged at Peaks 10a setting until 7.4a @ 15.6v... but then switched to 4a setting to lower voltage... charged until 4a @ 15.11v.

Fairly cold days this past week.

Today, 5 days since last top charge, Temps at about 34F, OCV was 12.83v. (No, that's not a typo.)

It appears, even at colder temps, my 6v CG-2's do not respond well to top charging at higher voltages. This past fall I discovered higher charge voltages led to lower resting OCV. I will let them sit for another week, and compare them at the regular 2 week interval. I hope to see self discharge back to where it was last winter.

I suspect the OP's batteries were not sufficiently charged before being put into stoarge... An incomplete charge by the B&D, followed by too low a voltage finishing charge (float, rather than an actual top charge) is the reason for the low resting OCV.

So, it appears both insufficient pre-storage charging as well as too high a voltage can both result in low storage voltages.

[MEXICOWANDERER]

A run of "X" feet (long distance) from batteries to inverter...

E=MC2 told you X gauge wire would work fine and it did. Then trouble arrived. You suspect the cables or a connection. Clamp the carbon pile wires onto the shut off inverter's connectors right over top the cable lugs. Twist the CP load knob to your theoretical E=MC2 amperage value and watch the volt gauge. Oooooooo, it's sagging way down. STOP! OR YOU'LL HAVE A FIRE! Unload the carbon pile and quickly start checking connections with your hand.

Properly sized and constructed electrical conductors DO NOT GET WARM. EVER. This testing is valid on a solar panel run and ANY OTHER amperage bearing power wire. Those wires are intended to pass a specific current. If they can not do that then you have a problem.

Even a marginally "bad" connection will heat up dramatically. Sometimes you'll need a helper on smaller wires but keep repeating the load draw and go down the line.

While some techs are still scratching their --- I have finished my repair and am on my way home.load testing cables is easy, with dramatic results and is infallible. I do not use the word infallible lightly.


Pssttt Sizzle Sizzle (obscenities) sure found that impossible-to-find bad place in a hurry, didn't you? Warm places are disasters waiting to happen.

[mena661]

Bump for MEX.

[MrWizard]

please elaborate
i have that tester
never thought of using it to test my solar setup
BUT all my panels are parallel

[MEXICOWANDERER]

This is where that carbon pile Harbor Freight battery tester shines. Connect it anywhere to in series parallel circuit and the slightest itty-bitty excess resistance screams it's fool head off. No subtlety here. Smoke, crackling noises, loss of connection.

[jrnymn7]

I need to wire things up to my new bus bars, anyways, so I'll pull everything apart and check everything then. Thanks.

[mena661]

I'd take a look at the cables and maybe even disconnect all the cables and check voltages on each battery. They should all be really close if not dead even. I know my bank showed surface charge even when one of the 6V was down in voltage due to a bad cable. What really tipped me off was the Victron showing a tenth or two of an amp continuously going into the bank. When my batts are full, the Victron displays 0 amps (takes a few days even after the SG says full).

[jrnymn7]

Mena,

Actually, it did occur to me yesterday that I should do a check with my clamp meter. I'm not sure how small a draw it could detect with any accuracy, though. It's display likes to jump around a lot, and I find myself constantly hitting the reset button. It's a Uni-T 40/600a. I'll give it a try sometime over the next few days, though. Thanks for reminding me.

I'll double check all the connections while I'm at it, too, but I haven't moved the rig since connecting things back up in series/parallel, which was not that long ago. And I'll check the inverter's ground while I'm at it. If that doesn't show any significant difference after a couple weeks, I'll even try disconnecting the inverter, etc., and see if that makes any difference.

Oh, and this past Sunday, when I was putting a top charge on the bank, I immediately noticed one battery taking .03 volts more than the others. This continued throughout the entire charge. All 4 were charging and dischargng equally until recently. It was one of the two 6v's I EQ'd back in the fall, so maybe it's going all girly-man on me? I have noticed I cannot get all things to agree, either. If the SG's are equal, voltages are slightly off, and vice versa. I've settled on equal voltages over equal SG's.

[mena661]

jrnymn7, do you have a clamp on meter? I have found mine to be priceless having used it to troubleshoot two bad cables on my bank.

[MEXICOWANDERER]

"This past summer they were over charged a lot, which resulted in excessive gassing, overheating, and electrolyte levels dropping below the tops of the plates on a few occasions"

Eventual antimony migration is inevitable with time and activity. Overcharging however gives the process a dose of vitamins and anabolic steroids.

One of the Exide labs on Mare Island specialized in testing of lead dioxide negative plates for the amount of antimonial contamination. Woe to the Captain of the boat whose batteries were overly contaminated before their time. A refit with all new batteries cost more than several new 2 bdrm homes. The admonishment of course was calibrated to the amount of shipping that went glug glug during the lifespan of the batteries or where the boat was patrolling. Fairbanks Morse engines, coupled to GE or Westinghouse motor generators could really -----slap the forward or aft bank. It was rumored that Dudley Morton abused the hell out of his batteries.

[jrnymn7]

I top charged all four 6v's as a bank, after having EQ'd two out of the four 6v's just a handful of weeks earlier. I hoped OCV would hold like it did last year, but it did not. Disappointed? Yes. Surprised? No.

Although, I still do wonder on occasion, if perhaps there is a very small leach draw happening, due to a loose ground or something? The inverter remains connected, and it is grounded to the chassis, but I'm not sure if that could be the case?

[MEXICOWANDERER]

Yes