P38A What can kill a battery?

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EntropyUK

Well-Known Member
Posts
467
Location
Hemel Hempsted
I need some guidance. Yesterday I was driving around doing chores did a couple of stops to shop without a problem. Went to the local supermarket and spent 10 mins in there came out to a dead battery. Got a jump start, drove it home, took 5 mins and turned it off. Tried it and car would not start.

Battery is only a couple of weeks old so will try and claim on warranty. Is there anything within the car systems that can kill the battery in such a sudden way? There was no battery light lit so no internal indication that the alternator was on the blink.

Also what checks do I need to run to eliminate the car from this equation? I have had a sudden battery failure many years ago so I know it can happen, just want to be sure before claiming under the warranty.
 
Batteries can just die without warning, internal failure
Charge it up overnight, connect up and measure voltage drop with headlights on for 5 mins. Turn headlights off and see what it recovers to
 
May just be a drain on it somewhere, 5 mins drive wont have added the charge to cover the jump start. Get a volt meter on the battery so you can see the before you start voltage and see overnight etc.

If you started the day literally with enough juice to crank it then did 2-3 stops I can see how you may have ended with less than enough but it does sound ****e for a new battery.
 
I'd be looking at the battery clamps as well. They're not a great design unfortunately.
Check the starter connections as well.
Check the alternator connections.
Check earth straps.
If you have multi meter, do a continuity test on the negative side.
body to engine,
Body to chassis,
Engine to chassis.
Continuity test plus side.
Battery to starter,
Battery to alternator,
Starter to alternator.
To make sure there is no breakdown in current passing between them.
Also check the battery,
Find a good earth and test the positive battery clamp and compare it to the battery's positive post.
Do the same with the negative side of the battery also.
This will tell you if there is a connection issue between the battery and it's clamps. 👍
 
I though I would resurrect this post rather than start a new one. I got to the bottom of the issue, the battery has stopped holding a charge and I think this is caused by the battery not being charged. With the engine running it was showing 12.5v across the battery posts and slowly falling and the battery light on the dash is off, thats why I did not know there was an issue until it wouldn't start.

I then put the multi meter on the alternator. +ve on the outlet post and -ve on the alternator body. This gave me 13.5V so I assume the alternator is running as expected. I was seeing 8v on the other screw post. I also bypassed the the alternator lead and connected a jump lead between the alternator and the battery connector. The battery across the terminals showed 13.5 volts so I rule out an earthing issue.

The only work I carried out near the alternator was replacing the glow plugs.

So, what do I check next? Does the alternator wiring go straight to the battery or via something else?
 
At least on the petrol, i assume the diesel is the same, one wire comes off the alternator direct to the battery, with a T off to the fusebox half way along
 
Hi, 12v systems should show 14.2-4 volts across the battery, I know my D2 & FL1 do so it seems a bit low & you won't always get a battery light on the dash for a failing alternator.
 
Have you done an earth leakage test ?
Make sure everything is switched off in the car, including interior lights etc. disconnect battery negative lead, and connect multimeter (amps) between lead and negative on battery. You should get less than 0.05 amps. If above this figure, starting pulling fuses to isolate fault to relevant circuit.
 
If it’s a diesel sounds like you have the original voltage regulator. Modern batteries require 14.4 set point. Original was 13.somesuch for old lead acid type. C9B67FDD-243C-4D94-858C-EC5641967606.jpeg
This is - by the way - information. It does sound like you have a drain of some sort and a decent run alone won’t charge the battery of a diesel P38 whichever regulator you have. This is why so many use a CTEK
 
EntropyUK said:
I though I would resurrect this post rather than start a new one. I got to the bottom of the issue, the battery has stopped holding a charge and I think this is caused by the battery not being charged. With the engine running it was showing 12.5v across the battery posts and slowly falling and the battery light on the dash is off, thats why I did not know there was an issue until it wouldn't start.

I then put the multi meter on the alternator. +ve on the outlet post and -ve on the alternator body. This gave me 13.5V so I assume the alternator is running as expected. I was seeing 8v on the other screw post. I also bypassed the the alternator lead and connected a jump lead between the alternator and the battery connector. The battery across the terminals showed 13.5 volts so I rule out an earthing issue.

The only work I carried out near the alternator was replacing the glow plugs.

So, what do I check next? Does the alternator wiring go straight to the battery or via something else?
Click to expand...
as others have said, 13.5 volts will not fully charge a modern lead calcium battery, 14.4 volts is really the minimum, 14.8volts is better. The MobiletronVR-VW010 i is a direct replacement for the regulator used on the diesel alternator.
apart from that, there is clearly a problem between the alternator and battery. The positive wire has been known to corrode away inside the plastic sheath. I would replace the wire from the alternator to the battery.
 
Datatek said:
as others have said, 13.5 volts will not fully charge a modern lead calcium battery, 14.4 volts is really the minimum, 14.8volts is better. The MobiletronVR-VW010 i is a direct replacement for the regulator used on the diesel alternator.
apart from that, there is clearly a problem between the alternator and battery. The positive wire has been known to corrode away inside the plastic sheath. I would replace the wire from the alternator to the battery.
Click to expand...
+1 on the mobiltron, easy upgrade and 100% worthwhile
 
EntropyUK said:
I though I would resurrect this post rather than start a new one. I got to the bottom of the issue, the battery has stopped holding a charge and I think this is caused by the battery not being charged. With the engine running it was showing 12.5v across the battery posts and slowly falling and the battery light on the dash is off, thats why I did not know there was an issue until it wouldn't start.

I then put the multi meter on the alternator. +ve on the outlet post and -ve on the alternator body. This gave me 13.5V so I assume the alternator is running as expected. I was seeing 8v on the other screw post. I also bypassed the the alternator lead and connected a jump lead between the alternator and the battery connector. The battery across the terminals showed 13.5 volts so I rule out an earthing issue.

The only work I carried out near the alternator was replacing the glow plugs.

So, what do I check next? Does the alternator wiring go straight to the battery or via something else?
Click to expand...

13.8V is the old alternator set point. Not enough for a calcium battery. You can replace the alternator regulator to give 14.3 or even 14.5V but it will only have the same power so takes longer to charge a big 1k CCA battery. Replacing the regulator is about £20 and will need to be done anyway. After that you're looking at parasitic drain or RF interference.
 
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