Vehicle battery appears dead but isn't

[Barnstorm]

Hi guys

I finished the conversion on my T6 - with a lot of help from members of this forum. I now have a strange problem, which has happened twice.

I have a Renogy DC-DC charger fitted with a solar panel connected. That's great for topping up the vehicle battery when not in use for a couple of weeks or more.

Today I went to the van, checked the Renogy monitor and it said both vehicle and leisure batteries were fully charged. I jumped in the driver's seat and put the key in. The dash lights came on and then instantly everything went dark. Completely dead. I checked the battery monitor and it said 2.5 volts.

This has happened once before and someone helped me out with a jump start. So I grabbed my mains battery charger and connected it up. After 30 seconds the battery monitor said 12 volts. So I disconnected the charger and it still said 12 volts. I put the key in and everything was fine - the van started first time. The clock had gone to 00:00 though.

It's like the van thinks the battery is dead when it isn't.

I really don't know where to start with this. Any ideas anyone?

Thanks

 

[roadtripper]

If it's happened before my suspicion is that your starter battery is dead and only holding minimal charge - voltage will look fine until you try to crank.

The XC70 I part exed to get the Caravelle did exactly the same due to being laid up during COVID, even with regular runs and a CTEK charger.

How old is the battery?

 

[Pete C]

Try something else. Put your ignition on and turn some lights on - what happens ?
I bet the battery voltage drops fairly fast.

I too think your battery is knackered.

Pete

 

[DXX]

Battery voltage isn’t a reliable indication of a batteries condition. It needs load testing.

 

[Dav-Tec]

Agreed that battery is fubar get it changed

 

[Pauly]

Only other possibility i can think of is a poor main earth but that would not affect voltage across battery terminals so depends where you measure from

 

[Dellmassive]

could be bad connections. . . or bad battery.

post some pics of the starter battery and Renogy and leisure battery.

 

[Ayjay]

I posted about it elsewhere here on T6F but my AGM leisure battery died on me a while ago and I finally got around to replacing it with a Renogy LifePo4. The old AGM one had been in the car for a while after it failed with the charge sort of kept up by the Victron and when I eventually took it out it was reading 13.4V or thereabouts. Just as a test, I hooked up a little 40W electric toolbox which worked properly about 4 pr 5 minutes but then slowly ground to a halt over the next 15.