On my third pair of house batteries in 9 months

[rallypanam]

Originally Posted by boywonder

I'm unclear on how you can draw a conclusion from this........it depends on the state of charge when you start........10 amps for 6 hrs is 60AH worth of charge. If you batteries are 120Ah, or 150Ah, etc. you have put 1/2 (or less) of their capacity back in. When my batteries are fully charged they usually read about 12.8V.........

They are meant to be 100Ah batteries, and I think they were only at about 12.4 when he pulled them from the van.. So theoretically still had ~75Ah in them.. so another 60+Ah should have been more then enough.

Now the interesting thing is that his last set registered 12.9 when charged, but when load tested showed 0Ah..

[rallypanam]

Originally Posted by rallypanam

Now the interesting thing is that his last set registered 12.9 when charged, but when load tested showed 0Ah..

Allow me to quote myself.

This part is interesting because I had the same problem with my AGM 4D. It would show 12.9V, seemingly acting normal, as soon as you put a load on it of a couple amps, it would knock it on its' ass and end up at 11.5V in a matter of minutes. Or if you just let it sit for a few hours it would drop to 11.5V.

I don't understand this.

[boywonder]

Originally Posted by rallypanam

I don't understand this.

Batteries die a slow, corrosive death....they basically rust* internally over time and recharge cycles.

*They actually form a sulphate layer...not exactly an oxide layer.....(I'm not a chemist..)

The chemistry (lead acid, alkaline, Ni-Mh, Li-ion, etc) determines the cell voltage....that's galvanic potential.

http://www.corrosionist.com/galvanic_co ... _chart.htm[youtube_id][/youtube_id]

When a battery ages, the plates corrode and form sulphate layers. Measuring an old near dead battery with a voltmeter does not draw any current (an ideal voltmeter has infinite resistance), so the small remaining non-corroded surface area gives the cell the correct voltage reading for no load.

However, if you put a significant load on the battery, a fresh battery has lots of clean plate surface area to allow zillions ions/electrons to flow producing lots of current with very little voltage drop.

In an old, crusty battery, the corroded plates have very little conductive surface area left, and simply cannot provide the zillions of ions/electrons needed to produce meaningful current. In this case, the voltage drops (sags) because there is just not enough ions flowing to keep the cell at it's design voltage.

Here is a simple mechanical analogy:

Lay out a garden hose and cap the end with a pressure gauge, turn on the faucet. The gauge reads 50 psi. Remove the gauge and lots of water flows.

Repeat the above but step on the hose until it's just got a tiny bit of area the remains open under your foot. Cap the hose with the pressure gauge and turn on the faucet.....you'll still see 50psi. Since no water is flowing the pressure is the same throughout the entire hose.

Remove the gauge with your foot still on the hose and you will get a mouse-fart's (there's that phrase again! ) worth of flow, since you are stepping on the hose.

Pressure=voltage and current=flow.

So, with a dead or almost dead battery, the cell voltages will be normal or close to normal under no load, but when you try to pull current out of it, there is just not enough conductive surface area left to provide sufficient current.

[rallypanam]

That makes sense, I think.

But how does a new (assuming they haven't been sitting in a warehouse for 5 years) battery get to this point without draining it first? gcvt's latest set never went below 12.4, yet seem to be dead.

[boywonder]

Originally Posted by rallypanam

That makes sense, I think.

But how does a new (assuming they haven't been sitting in a warehouse for 5 years) battery get to this point without draining it first? gcvt's latest set never went below 12.4, yet seem to be dead.

....how many ways can a battery die........

This should keep you busy for a while.......the interesting stuff is near the bottom of the page.

http://www.mpoweruk.com/failure_modes.htm

[Scalf77]

Using voltage alone is very difficult as a measure to how well the battery is charged. First and foremost there are multiple voltage charts, some such as this one are based off of the battery being in the RV.

(If battery was just charged, it needs to set for 2 to 3 hours)
Other charts are based off of being out of the RV or open circuit Also when you charge the battery you will need to make sure that you don’t measure the surface charge as it will make the readings higher then expected.


Proper way to rid yourself of surface charge:
1. Allow the battery to sit for six hours with no load or charger connected, or...
2. Apply a 25 amp load for three minutes and wait five minutes, or...
3. With a battery load tester, apply a 150 amp load for 10-15 seconds. (12 volt side of life)





For good reading on 12 systems I recommend the 12 volt side life
http://www.marxrv.com/12volt/12volt.htm

-greg

[rallypanam]

Originally Posted by Scalf77

Using voltage alone is very difficult

So you gotta wait 3 hours or so after charging to even look at the voltage. That makes sense.

[gcvt]

Just got back from the local Interstate distributor. They load tested both batteries. Turns out one battery was bad and the other one was fine. Got a replacement so I should be good to go.

[BroncoHauler]

Originally Posted by gcvt

Just got back from the local Interstate distributor. They load tested both batteries. Turns out one battery was bad and the other one was fine. Got a replacement so I should be good to go.

Did they load test the new one?......

[gcvt]

Originally Posted by BroncoHauler

Did they load test the new one?......

LOL, yes. ~98%