Battery with one bad cell - warranty or my fault?

I've got a OE spec VW 80AH battery in my 02 Golf. It replaced the original battery in December of 09 (original went 6.5 yrs). Hygrometer indicates it has one bad cell. I discovered it because it would not start when I returned to the airport after 8 days (temps were in the 20s, but had not been that cold for the duration).

I would expect better than 3 years for the OE battery, but I wonder if I have some responsibility. Could what I put it through in May, or lack of attention to electrolyte this year have toasted it?

Is there a chance of a desulfating battery tender bringing the battery back?

Background:

In May I had a 2 week trip and left the lights on at the airport (drivers door interlock is out) resulting in a very dead battery. Dead enough that after driving for 40 minutes after the jump, it still wouldn't re-start and had to be jumped again to get home. Battery got charged with my "automatic" (no choices in charge rate, but has charge and maint modes) battery charger, but I did not check electrolyte levels. I also did not check electrolyte levels for the first 2 years of the battery.

After the most recent no-start I checked things out. Electrolyte was low in all cells (last checked and topped last Dec '11) Maybe 1/2 cup total to fill all 6. One cell has very low specific gravity, the other 5 are good. Charging system voltage is a steady 14.3 volts when the engine is running.

Right now, if I'm driving the car regularly it is starting w/o a problem, but if it sits for a bit it barely turns over after the glow plug light turns off.

I think you toasted it.

I say take it to the dealer and tell them it has a bad cell and ask them to warranty the battery. Let them decide if they will pro-rate the charge towards a new one. My guess is you did not kill just one cell from the deep discharge (all should be equally affected if you caused damage).

Look at it this way, maybe you caused the early failure, maybe not. But if you did, how many times do you think the dealer accidently caused damage to a customer's car and said an additional part needed replacing and charged them for the dealer-caused replacement? And if you did not cause the failure and did not ask for a warranty claim, that's not right either.

Also, it's the dealer's job to ask you the correct questions. If they asked if you let the battery run down and how long it was discharged, I'd be honest and hope for the best.

--Nate

Excellent advice PDJetta. Will do.

Full discharge of a regular lead-acid battery usually kills it, particularly if it stays that way for any period of time.

Richy_T said:

Full discharge of a regular lead-acid battery usually kills it, particularly if it stays that way for any period of time.

Click to expand...

That is my thought too, having done it myself on some deepcycle storage batteries on a solar setup I once had.

Thought I would update this thread with my experience.

My battery was out of warranty, so no option with a pro-rated replacement. I know the parts guy at the dealer where I got the battery, and he treats me well.

I decided to buy a BatteryMinder de-sulfating battery charger. After letting the battery charge for 72 hours it significantly improved the bad cell in the battery. My hydrometer readings went from fair to good. There is a noticeable difference in cranking when cold, however I don't know if the battery would be strong enough if the car sits unused for 2 weeks.

Concerns right now:

My charging voltage measures 14.3v. This seems high. I haven't found the spec for this car. Anyone know?

I had to top my electrolyte level twice. Once when I noticed things the first time, again after I had charged with a run of the mill 2A Interstate battery charger. My concern is that I'm over-charging the battery

The battery drain when the car is sitting seems to be within spec. It is 30-40mA when the hood interlock is disconnected, and the car is closed and locked.

I will see if I can find the spec on charging voltage, and determine if I have an issue there.

I'll wait till the car can sit for an extended period of time and see what happens (I have a really good booster pack to get me home if necessary).

JP

Alternators usually put out 13.5 - 14.5 volts at idle at the battery terminals. It's a function of the voltage regulator inside the alternator. All is good.

Thank you aja8888!

JP

Yep, it's been my experience, if an auto battery is totally discharged, for whatever reason, it will never be the same. It will have less hump, cannot crank as long, cold affects it tremendously, etc. A long very slow re-charge (300 miliamp or less) is better than forcing 2 to 10 amps on it for a few hours.

Thanks Andy - that is what I suspected. I might be able to get it through the winter and get another season out of it.

JP

The problem of having a state of discharge is that there will end up being physical damage to the plates. The length and depth of discharge as well as the physical layout of the plates and their construction will determine how much damage is caused.

In flood cells, the plates are arranged vertically, so that when the sulfate crystals form and damage the plate surface, the crystals can break off and settle at the bottom of the cell, where it won't get in the way of the plates working. With sufficient settling, the sulfur from the electrolyte is removed, so it is no longer as acidic as it was. Therefore the ability of the cell to make electricity is compromised. The settling of the sulfate crystals also implies that there is lead involved, which means the plates are losing their major constituent. This also makes it more difficult to get electricity from the cell.

Cells can be desulfated, but if and only if the sulfate crystals are still attached to the plate surfaces. Once they're at the bottom of the cell, there is no recovery for them.

Charging a battery takes up to 14.4 volts; with current construction (i.e. calcium alloyed in the lead for strength) this is the point where water starts to get heavily involved due to electrolysis and generate gas. If the amperage is low, and there is a catalyst at the top of the cell, the catalyst can recombine the hydrogen generated back into water and prevent water loss. This only works if the overcharging is at an amperage low enough that the catalyst can keep up with the gasses evolved and not overheat.

So basically, if the charging voltage put out by the alternator while the engine is running is 14.4 volts or less, you're OK. If it is less than about 13.9 volts, you will never get a full charge on the battery.

If you have the battery on a charger trying to desulfate it, please check the electrolyte levels in all cells often.