Dead cell or something else?

[randomvolvoowner]

Hi All,

Just wanted some opinions from some experts.

My 2008 Diesel V70 has always been reliable, but this morning it randomly wouldn't start. This has only happened once before just over a month ago.
Basically I get in, key in the slot, foot on the clutch, press the button. It kinda feebly goes to turn over, but kind of a weak 'cough' and doesn't startup. I keep my foot on the pedal and it keeps retrying a few times, but to no avail. Eventually there's not enough juice in the battery so it gives up trying. Usually its fine and starts straight away.

Tested the battery voltage (before trying to jump start), it was about 12.3v.
Got my neighbour to jump start me, it started straight away.

I'm thinking a dead cell in the battery maybe. Before I sink a fortune on a new battery, just wanted some opinions in case there are other things to check first.

Any help would be greatly appreciated.

[RickHaleParker]

Cells are ~2.1V each. 6 * ~2.1V = ~12.6V
If one cell was dead and the rest where good the voltage drop would be 5 * ~2.1V = ~10.5V.
12.2V indicates the battery is ~50% discharged. Which is a real deep discharge for a starter battery.

A good bet is: the battery is heavily Sulfated, a buildup of Lead Sulfate Crystals. Which is caused by leaving a battery discharged. The deeper the discharge the faster the buildup.

Put it on a battery charger as much as you can for a week. Float charging will convert the Lead Sulfate Crystals back into lead if they are not too hard. A month or so might might convert hard Lead Sulfate Crystals back into lead.

I have a battery I brought back to life from 150 millivolts (0.150V) 100% discharge after it sat dead for better then 6 months. Took weeks on the charger but I got it done.