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teddyu · 09-26-2014, 06:49 PM

Old Navy submariner electrician here that has been traveling cross-country. This developed on this trip, the coach sometimes started on the chassis battery some times not. The aux start would get the coach started sometimes. Running the generator and powering the battery systems with the converter would always start the coach. Did all the normal things: cleaned battery terminals and all of the connectors in between the chassis battery and the starter solenoid. Still did not fix the problem. Pulled out the handy-dandy battery charger and charged the battery directly overnight. Open circuit battery voltage was 13.2VDC after charge, specific gravity was about 1.275 all cells. Still would start the coach with out some help. At my wits end, I drove the coach to Autozone (battery was an Duralast 65) and removed the battery to have it shop tested. Lo-and-behold, the battery tested fully charged and and voltage at 13.2vdc, but the load test determined the battery was bad. Replaced the battery and was on my way. I think the problem may have been a broken seperator or failed grid, not sure. I'm sure somebody will have some opinion as to what failed.

The reason I'm sharing this is that all the tests I conducted on the battery showed the battery good, but the load test was the definitive test to determine the true condition of the battery. JM2¢...

Skip426 · 09-26-2014, 07:12 PM

[QUOTE=teddyu;2245185. I think the problem may have been a broken seperator or failed grid, not sure. I'm sure somebody will have some opinion as to what failed.

The reason I'm sharing this is that all the tests I conducted on the battery showed the battery good, but the load test was the definitive test to determine the true condition of the battery. JM2¢...[/QUOTE]

X2, if it hasn't been load tested , it can't be ruled out as the problem.
A volt meter is not a load.

Bfmorgan · 09-26-2014, 07:45 PM

The failure you experienced is not an unusual failure. Most batteries will reach a point where they are able to provide a reasonable voltage, but the voltage will drop drastically as soon as you apply a load. Harbor Freight will put a battery tester that puts a 100 amp load on the battery on sale for around $18-$20.

IMDSailor · 09-27-2014, 05:40 AM

Can you load test 6v batteries individually or do they have to be in pairs to make 12v?

Thanks

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**pasdad1** · 09-27-2014, 06:07 AM

I guess that depends upon if you have a 6 volt capable load tester ...... they exist since most golf cars run on a bank of 6 volt batteries. (Some golf carts use 8 volt batteries too)

jesilvas · 09-27-2014, 06:21 AM

Good reminder that batteries commonly can have a good surface charge, but under load are shot.

OLYLEN · 09-27-2014, 07:13 AM

Another tip is if in the fall as the weather runs cooler the vehicle just doesn't sound like it is turning over quite normal. Have the battery tested, the cool temps show batteries going bad before a total failure.

LEN

TQ60 · 09-27-2014, 09:08 AM

Battery was degraded or sulfated.

Imagine a class of water as a battery.

Make a line and fill with water.

Water is your charge capacity and the line represents the

Pour this water into a mesuring cup.

Now place a bunch of rocks or gravel in glass.

Now pour water from measuring cup back into gravel filled glass until it is at same line and observe volume still in measuring cup.

The charge voltage is still the same but there is a lot less charge in the battery as seen by water in measuring cup.

The gravel represents sukfation or degradation of the typical lead acid battery.

All of them do it over time.

And voltmeter or specific gravity measurements will not usually indicate it but the test you have performed by filling with water represents a load test where you can place a load on charged battery and see how it preforms.

Simple...?

IMDSailor · 09-27-2014, 09:13 AM

Quote:

Originally Posted by TQ60

Battery was degraded or sulfated.

Imagine a class of water as a battery.

Make a line and fill with water.

Water is your charge capacity and the line represents the

Pour this water into a mesuring cup.

Now place a bunch of rocks or gravel in glass.

Now pour water from measuring cup back into gravel filled glass until it is at same line and observe volume still in measuring cup.

The charge voltage is still the same but there is a lot less charge in the battery as seen by water in measuring cup.

The gravel represents sukfation or degradation of the typical lead acid battery.

All of them do it over time.

And voltmeter or specific gravity measurements will not usually indicate it but the test you have performed by filling with water represents a load test where you can place a load on charged battery and see how it preforms.

Simple...?

The specific gravity checks as does the SoC. I'll get a load tester.

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TQ60 · 09-27-2014, 09:24 AM

Also note that your microwave is a great load tester...for coach batteries.

Best to do with fresh batteries then repeat later to confirm performance.

Get bowl of water large enough for 5 minutes of use.

Make sure batteries fully charged...float charged a day or three.

Turn everything off then turn on inverter and measure battery voltage.

Place water in microwave on high for 5 minutes and recheck voltage when finished.

Record this time in your log book.

The voltage will drop a bit over time but when the voltage drops a bunch more than before then battery is starting to fail.

The key here is repeatability. ..always full charge on battery and same setup process with same time so the test is same every time.

When the results change the battery is causing said change.

wa8yxm · 09-27-2014, 09:29 AM

As Lead acid batteries age sulfate builds up on the plates,, So long as any part of the plate is in contact with the electrolyte (Acid/water mix) the battery will charge and show as charged. But as the sulfate builds up on the plates the "internal resistance" of the battery (actually the quotes are not needed as that is what it is called) increases, thus the cranking amps start to resemble a rock in free fall (GOING DOWN They are).

This, is not a weird battery failure,, It is in fact the most common battery failure. Some chargers have a "Desulfate" mode, this is supposed to delay this type of failure.. Also Equalization may delay it.

Key word is DELAY, however.