What causes individual Cells to go bad?

[The Ice Man]

Need insight from you battery gurus.

I try to take care of my batteries. I check water level every month and use a hydrometer every 2 to 3 months.

This AM 9 cells read specific gravity at 12.50 to 12.60 and 3 read 11.50 to 11.60 which is weak.

Batteries go from 12.6 -12.7 V to 12.1 V in about 5 days with the switch in "Store."

Batteries are dated Jan, 2015. So probably due for a swap out anyway.

Why would just a few cells go bad and not all?

Also, in another thread, the Sub-Woofer is mentioned as a parasitic draw. How do you turn off the Sub-Woofer?

[dznf0g]

Sulfate Crystals can form as well as shedding of lead material from the plates. These conditions can cause several issues like weakening the acid concentration to causing partial shorts in the cell.

Some other things that can happen, but not too frequently include conductors between cells coming loose.

Most common is sulfation. Occasional equalization charge cycles can help as well as "de-sulfators" and de-sulfation chargers. I have used BatteryMinder technology for about 7 years now, and I believe it to have merit.

Oh, about the sub. Mine didn't have one, so I installed an aftermarket speaker and amp. The amp is switched to the radio power button and relayed to the positive buss bar. When the radio head is popped off, there is no parasitic draw at all. So, when in storage, I have all items isolated, except there seems to be a keep alive circuit in my brake actuator....probably not a good idea to switch that one. I have about 150mA parasitic draw total...but that's with the battery monitor powered up. Mfr says when it's asleep it pulls 10mA but they couldn't tell me how much when the screen is lit.

[Al and Missy]

One cause of bad cells in wet cell batteries is plate material flaking off, falling to the bottom of the cell and shorting, or partially shorting, the cell. Current flows through the flakes all the time, discharging the cell prematurely and stealing some of the charge current. Also, cells can get coated with sulfate, which may be able to be restored with an "equalization" charge. Some converters have this capability, some do not. I don't know if this can be a "selective" fault, i.e. in some cells and not others.

My trailer doesn't have a subwoofer so I am guessing here, but if it is a parasitic draw it must be wired to the battery side of the disconnect switch. It will probably have an inline fuse so it should be easy to find by tracing wires on the battery side of the switch or the battery. Several things may be connected this way, i.e. the subwoofer, the breakaway switch, and/or the tongue jack.

To fix it you can wire in a switch or move the connection to the trailer side of the disconnect switch.

Al

[rmkrum]

Meh, Al got there first...and he's also right on the 'sulfation' issue as well...

One of the things that can kill individual cells in a lead-acid chemistry battery is a phenomenon in flooded batteries known as 'shedding'.

As a battery is used, in varying temperatures, subjected to vibration and shocks, the plates can shed tiny bits of metal, usually the lead paste that is pressed into one of the plates. The particles migrate to the bottom of the cell, where there is a 'pocket' under the plates that allows the particles to fall harmlessly out of the way, to a point.

When enough shedding occurs, you get a partial short in the cell, and it rapidly deteriorates because the partial short shunts charging current outside the plates. The cell slowly fails to achieve full charge. It gradually gets worse, and the cell eventually fails completely...

AGM batteries have less of this, but it still happens to some extent.

Another failure mode is dendrites, which are skinny crystals of metal that grow through the separators and short out cells. This happens a lot in Nickle-Cadmium batteries, for one.. Also happens to be one of the more interesting failure modes for modern printed circuit boards assembled using lead-free solder. The tin in the lead-free stuff loves to form dendrites and short things out over time...especially in the presence of moisture and uncoated circuit boards. Sometimes going over a corroded circuit board with old-fashioned lead-based solder and fresh flux can rejuvenate a failed PC board. Used to fix my old Volvo relay assemblies that way, if the cover could be pried off easily.

[JohnTF]

Been in the auto repair bis for many decades , any battery is only as good as its weakest cell , so one goes bad - the whole battery is bad .
Then to add to that , after replacing 100s or 1,000s of batteries in cars / truck etc. , and solar systems over the last 35+ yrs.
From memory , its is almost always the the cell on the positive end of battery .

[OTRA15]

Great comments so far! FYI an online resource for general battery info.

Why they go bad: http://www.batteriesnorthwest.com/ba...cfm?TID=3#ANC3

Note overheating, freezing, vibration, and overcharging as some possible causes. I assume that the RV life increases these risks a bit.

Sulfation: http://www.batteriesnorthwest.com/ba...cfm?TID=5#ANC5

Can we add "manufacturing defect" to the list?

Good luck,

Peter

[GM Airstream]

Several good articles on bats.... and yes you can get sulpfat anytime the bat gets over 85 deg temp... here is what I have on the subjects... and yes I keep a de-sulphnator on the bats when not using them to keep them in the best shape they can be in for their age..

[dznf0g]

Btw, BatteryMinder makes a desulphator WITHOUT charging capability. I have one permanently installed on the AS and TV.

[Bgibbs]

I would try a charger from Pulse Tech. It will oftentimes cure a bad battery. Used by the military, airports and fire departments to keep equipment that is used infrequently “ready to go”. Check em out.

[The Ice Man]

Gurus to the rescue. Thanks all.

The links have been followed and bookmarked and the PDFs downloaded.

Appreciate the help.

[The Ice Man]

Now to the Sub-Woofer issue. Any insight?

[uncle_bob]

Originally Posted by The Ice Man

Now to the Sub-Woofer issue. Any insight?

Hi

It's wired into the 12V distribution system. Find the sub in your trailer and put a manual switch in the power lead. AS never did anything the same way twice so it will always be a "dig in and see" sort of thing. Your inverter is likely a much larger parasitic load ( even when off) than the sub ....

Bob