300tdi Battery problem

Hi guys, I'm a newbie when it comes to electrics however I like to give everything a good go.

So the existing battery in my defender failed beyond the point of saving even with my smart battery charger attempting to save it. So I had to buy a new one, everything was ok for about two days and then it was completely flat. I recharged it but something is still drawing enough power to cause the battery to go flat. As far as I know the only things drawing power when it's off are the clock and a tracker which happens to be wired to the clock. Any ideas on fault finding for this? A friend suggested an isolator switch but then the permanent live feed for the clock/tracker would be rendered useless. A dual battery system maybe? Any photos or diagrams for this are very much appreciated.

Is it going flat or not charging properly? Have you measured the key off current draw from the battery to see what that is?
Whats the charge voltage when the engine is running - have you got a voltmeter on it? Don't trust the light - that can go out and the battery not charge properly.

Yup, if it isn't something draining ... then it must be something not charging ...

Dipps you are a STAR ! You do have a way of stating the obvious !

Magicgrotto said:

Dipps you are a STAR ! You do have a way of stating the obvious !

Click to expand...

It's a gift ...

Thanks for the replies guys. If I leave the battery connected it goes flat so there must be some sort of parasitic drain. The alternator appears to charge the battery fine as I have connected it to my battery charger after going for a longish drive and it's back at 100%

If I get hold of a voltmeter how do I test what the battery is drawing when the engine is switched off?

Ok, a battery charger isn't a good way to test this. It does sound like a drain somewhere though.

If the battery is charged and connected, does the alternator get warm, especially around the back behind the plastic cover? Check it after the engine has cooled down obviously the exhaust can mask this.

Also where are you in Leeds? PM me and I can probably drive over with some test gear I'm only about 5 miles from the city centre if needed.

Dual battery setup is in the CFAQ section.

To check current drain, remove battery terminal (either one) and connect a multimeter ( not voltmeter) between the battery post and battery lead. Ensure it's the correct way round (polarity) and set the multimeter to AMPS!

And dont try start engine or even turn on heater or headlights because you'll melt the multimeter

Grem said:

And dont try start engine or even turn on heater or headlights because you'll melt the multimeter

Click to expand...

Wot he said... it is ONLY to be used to check current drain with all systems turned OFF

What you can then do is pull one fuse at a time (then put it back in), when you see the current drop you'll know what circuit the drain is on! That'll narrow it down to a few possible things. Pretty sure @Kwakerman taught me that!

Al2O3 said:

What you can then do is pull one fuse at a time (then put it back in), when you see the current drop you'll know what circuit the drain is on! That'll narrow it down to a few possible things. Pretty sure @Kwakerman taught me that!

Click to expand...

Take the alternator cable off first. Unexpected battery drains are often due to the wonderfully high quality Lucas rectifiers not actually rectifying as well as they could.....

Al2O3 said:

What you can then do is pull one fuse at a time (then put it back in), when you see the current drop you'll know what circuit the drain is on! That'll narrow it down to a few possible things. Pretty sure @Kwakerman taught me that!

Click to expand...

That's a great idea, at least I can try and narrow it down. Iv borrowed a multimeter from my neighbor, so I guess tomorrow evening is booked up. Thanks for everyone's suggestions and tips, I'll keep you posted with how I get on.

So I stuck my multimeter between the battery's negative pole and the cars negative lead and got a reading of 12.21v (with the engine off) I'll start pulling fuses next...

Jam5good said:

So I stuck my multimeter between the battery's negative pole and the cars negative lead and got a reading of 12.21v (with the engine off) I'll start pulling fuses next...

Click to expand...

If you want to measure current drain, you'll need to use the AMPS scale on the MM - as recommended above in posts 8 through 12.

a battery drain unless obvious like a light on will usually have windings as the cause alternator favourite but can be heater motor or relay etc

Jam5good said:

So I stuck my multimeter between the battery's negative pole and the cars negative lead and got a reading of 12.21v (with the engine off) I'll start pulling fuses next...

Click to expand...

You need to check the drain, if there is one. You should be checking the amps.

Have a look here. Make sure to use the higher amps scale or you may blow a fuse on your multimeter.


Cheers

Cheers guys, might help if I read through this thread before going in guns blazing. Very helpful video, rechecked with amps this time reading 3.88

3.88 Amps !?! ?!? - with everything orft ????? ... Houston, we have a problem !

Did you disconnect your alternator yet ? ( and insulate the live wire for safeties sake )

I suspect new rectifier required

Jam5good said:

Cheers guys, might help if I read through this thread before going in guns blazing. Very helpful video, rechecked with amps this time reading 3.88

Click to expand...

Sounds like a rectifier to me.....

Start the car, and then put the voltmeter onto the AC voltage setting, probably 20V range to start with. Measure the voltage across the battery. If the rectifier has gone pop then you will get a large voltage ripple of a few volts to perhaps as much as 30V. If you do then it's new rectifier needed for sure.

Please note when doing this you will see a SMALL AC voltage even if everything is OK - perhaps as much as a volt. It's if it is significantly more than this that indicates a problem - if it is your rectifier with that current drain I think you are going to see 20V or more AC.