Completely dead battery ? but nothing at all - Xantia 1.9TD

[juraj]

Oh goodness, will it ever end?

This morning I went to start the Xantia, no central locking, no ignition lights, no radio, I thought must be some main fuse.

Nope the battery is so dead shorting it with a wire produces no spark, multimeter next -

0.03 V !!!!!!

I have never seen a battery so dead, normally if the lights are left on say the next day it has 7-8V but 0.03V???

The car just did a nice trip to stanstead airport and back to london was parked and 24 hrs later this.

The battery has given no sign of this impending failure, prior to this it cranked the starter very powerfully and quickly.

Can a battery just collapse like this? I have not seen it before, ususally they get weaker and weaker over time.

But there is one complication, on the weekend the car started to mysteriously crank over really slowly, so I took it out charged and no difference, I thought maybe starter is going, but before removing he starter decided to check all connections, the main earth strap from battery (-) to gearbox had a poor connection, if i touched it to another point suddenly fast cranking, so I relocated the earth strap and since then perfect motoring all week till now.

Even if some component failed and started to draw on the battery constantly I would expect to find it with about 6-7-8V but 0.03V?

Any ideas?

bye

juraj

[RichardW]

Modern batteries all seem to go this way. OK one day, pancake the next. There is some sort of internal short / failure, hence no volts out of it. New one required

[juraj]

hi Richard

its just occurred to me that

1. i didn't remove the battery terminals, as i was in a rush and measured the 0.03V with them connected, thus if there is an external short in the car this could be causing such a low reading, but as you say modern batteries,

2. when i charged the battery on the weekend, it didn't need it, as the slow cranking was not a battery but poor earth, so i most likely charged a fully charged battery, perhaps i overcooked something, but why would it take 5 days to show up?

thanks for your advice,

bye

ps what is a typical value of current drain when the ignition is off, ie by the clock, the radio memory, etc, 10mA?? have no idea

[MikeT]

Don't quote me on this but I seem to have a vague recollection that a faulty alternator can short out a battery in double-quick time?

But the reason I'm replying is more related to this little gem of information I found regarding earthing points and cooling system corrosion that you may want to consider once you've finished with the battery issue....

"Aluminum is more vulnerable to electrolytic corrosion .... because aluminum is a highly reactive metal. When the corrosion inhibitors are used up and the pH of the coolant drops to 7 or below, aluminum becomes a sacrificial anode and is eaten away.

This same type of corrosion can also occur even when the coolant is in good condition if the engine does not have a good ground connection. Voltage from the charging system will flow through the coolant to ground, creating electrolysis corrosion that attacks the components in the cooling system.
"

[CitroJim]

Hi Juraj,

If you had a short of sufficient magnitude to drop the battery PD to 0.03V in such a relatively short time, I think your car would be a smoking ruin by now

As Richard says, this is how modern batteries die these days. Seen it several times.

Normal ignition off current draw will not be much and will be measured in milliamps (mA). I'd say at a guess, around 100-200mA.

Mike,

A short caused by failure of the blocking diode in the alternator will quickly reveal itself through a very hot alternator and a massive spark as you go to connect the battery.

Aluminium corrosion: Very interesting. One is given to speculate if this is, in part, why matrixes fail...

[juraj]

thanks jim

actually when i first saw the virtuall zero reading i thought there must have been a massive drain overnight and i started looking for burnt wiring or molten insulation even struck me that there was no burnt electrics or burnt plastic insulation smell,

well modern batteries!! its not very user friendly, an 'older' battery would give you plenty of warning, would fail to hold its charge, would need regular charging etc, but this? the battery behaved that morning like a very good one, so no matter how you prepare for a long trip etc you cant rely on your batteries behavior in the last few days or weeks to gauge whether it will take all the way there and back,

ok thanks guys,

i dont know about the coolant theory as i cant see how the coolant would provide a path to ground, after all if the engine is poorly earthed so will the coolant wont it? arent they really one system at the same potential?