Strange battery failure mode?

Question

The (original) battery on my 9 yr old Mondeo diesel (171k miles) has recent ly failed. No complaints over longevity but the way in which the battery fa iled has left me puzzled.

The car, having started fine every morning (with one exception -see below), failed to turn over at all one morning last week. The dials had a hissy fi t and there was much clicking from behind the dashboard. Measuring the batt ery showed 9.5V. I put the charger on it and left it for an hour. Voltage b ack up to 12V (still below fully charged but enough to start the car I thou ght) but again the same symptoms on trying to start it. Breakdown man calle d and he got it stared by jumping from his lorry. He diagnosed a dead batte ry and I went and did a click and collect for a Bosch from the local ECP sh op and was on my way in 45 mins.

Now, 2 months ago the car struggled to start. Assumed it was just the batte ry on the way out so drove around for 15 mins before parking up and doing s ome shopping. Came back to the car and it would barely turn over and after a couple of attempts gave up and I called the AA. He ran a battery check, p ronounced the battery fit and well and after whacking the starter motor a f ew times we got the car started.I also recently came back from a 3 week hol iday and the car started fine first turn.

Like I said - I can't complain about having to change the battery which has managed in excess of 6000 starts, but I was surprised that I didn't get an y notice of its impending end of life by say more laboured starting or othe r symptoms. It just fell off a cliff. Is this normal for the silver calcium sealed types?

Tim+ · Accepted Answer

Dunno about silver calcium but it's certainly common for lead acid batteries to just "die". I think the plates become more brittle with age and eventually vibration causes a fatal internal crack. Tim

Peter Hill · Answer

> has recently failed. No complaints over longevity but the way in A shorted cell will be just like a switch.

Etaoin Shrdlu · Answer

When mine packed in a few months ago, I thought the computer had gone bonkers. I turned the key, and the interior light came on, a lot of weird clicking noises came from the dash, and the dash lights were doing some sort of weird dance. Before that, there was no warning at all that it was on its way out. It was about 12 years old, though :-)

Mrcheerful · Answer

Definitely a quite common failure mode. My sister asked me to get another battery for her 2010 Citroen C4 as I was going to visit her the next day. I was a bit surprised and took various testers with me. The battery was the original ( I expect) a heavy duty Varta . On test it showed 9.2v. I got it started and checked the charging which was fine. Fitted the new battery. When I got home I charged the old battery till it said it was finished (few hours) and checked its load capacity and voltages, all seemed normal, left it overnight and rechecked, back to 9.something volts and no oomph.

As to your starter, it needs a rebuild, the other thing that can happen on those is that dual mass flywheel failure can release swarf which goes into the starter.

Chris Whelan · Answer

[...]

It's not related to the battery type, it's just normal for modern cars.

They start so easily, and turn over so freely, that they will start with a battery so knackered that it would struggle to even crank an engine of an earlier era. Additionally, modern alternators are so powerful by comparison with earlier ones that they will successfully recharge a very flat battery to its maximum potential (pun intended) in a short space of time.

Chris

Kevin H · Answer

Once the car was started I drove it to the garage (followed by the AA who then gave me a lift home) I use and they fitted a new starter the next day.

Strange battery failure mode?

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