Battery Drain 4.6 Thor

Hi guys, I know its been done to death but I have a problem with my rangie's battery going flat after a very short time.

99 Thor 4.6 HSE

I've had the car a year and to be honest it wasn't much of a problem for ages, however the battery was small and old and after 10 days or so it seemed to flatten it. The car never forgot the window settings or needed the EKA code or anything just sometimes needed a jump. (70ah battery)

Anyway I figured this was a weak battery so I bought the big mega 110Ah battery and put that in. It needed the EKA code that time, no problem got it all running. But it now seems worse than ever, I tried to use it yesterday and it had been 6 days since I had used it and it was flat (alarm LED still flashing) but wouldn't unlock on the fob and the message center showing key code lockout as soon as I unlocked the car. Almost every time this is flat i need to enter the EKA code which is very annoying especially as it never used to do it!

Other information SOMETIMES if you turn the ignition on but don't start the car it comes up with Alternator Fault on the message center. It always clears and I've never worried much about it because it manages to recharge the battery very quickly.

The problem is I don't actually use the car much or go very far in it, how long should it take to recharge the battery? The last time it was flat I did a 16 mile journey out of my way just to put some in it but it doesn't seem to have helped. Often the use I have for it is when Its got a job to do, or something to move and it isn't half annoying having to go through the messing about of jump starting and the eka code every time.

I was wondering is there a way of charging it through the tow bar electrics then I could just discreetly plug it in when its at home and keep it topped up?

I havn't checked the becm for battery drain issues but I have disconnected the RF aerial to try and help but it doesn't seem to have made much difference.

Whats the best way to test the new battery and alternator?

If a P38 say's "Alternator Fault" 100 to 1 there is an alternator fault and alternator faults are a common battery drain problem.
Need to check the output voltage at the battery at 2K rpm.

No problem, is it best just to get a new alternator for it and see how that goes?

if the alternator is on the fritz, then yes, that's the way to go.

You also have to bear in mind that turning over a v8 for short trips takes a fair draw off the battery, so lots of little short trips don't give enough for the alternator to recharge the battery, the range rover has a lot of electrics going on, so you need at least a 15 minute trip with no electrics on, or it will just keep taking a draw off the battery

ukadamwest said:

if the alternator is on the fritz, then yes, that's the way to go.

You also have to bear in mind that turning over a v8 for short trips takes a fair draw off the battery, so lots of little short trips don't give enough for the alternator to recharge the battery, the range rover has a lot of electrics going on, so you need at least a 15 minute trip with no electrics on, or it will just keep taking a draw off the battery

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Yeah I know this its what I've been working towards as well, I did take it for a 40 minute drive the other day which should have put something in it but it didnt seem to make much difference. the problem is its a third car so not often used, and the jobs it is used for are not big ones.

Assuming the alternator was OK, and its 150ah am I correct i thinking it would take around 40 minutes to charge a 110ah battery. Is that how it works?

I believe its not an awful job to fit an alternator so I think I'll get one and fit it and go from there - a new alternator can't hurt can it!

about 30 minutes to change the alternator !

At least that's about what it took me to one of ours the longest time was getting the belt on/off doing it solo !

we have a bit of a collection of cars so sometimes it can take a while for one to get used. i have installed the C-Tek plug on all our cars.. including the range rovers



So it's pop the door, plug the charger in shut it and thats it.

The charger is 50 quid and for me that cheaper than keep replacing deep discharged batteries!

quavey said:

Yeah I know this its what I've been working towards as well, I did take it for a 40 minute drive the other day which should have put something in it but it didnt seem to make much difference. the problem is its a third car so not often used, and the jobs it is used for are not big ones.

Assuming the alternator was OK, and its 150ah am I correct i thinking it would take around 40 minutes to charge a 110ah battery. Is that how it works?

I believe its not an awful job to fit an alternator so I think I'll get one and fit it and go from there - a new alternator can't hurt can it!

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It would take your alternator around 8 hours to bring the battery to 90% charged
Why waste cash on a new alternator without first checking it's at fault?
You can get overhaul kits for alternators

the alt can still charge a batt but be faulty..if the rectifier pack is faulty it canl put out a healthy charge but also allow the batt to drain when engine off..
one way to check, (but does require batt being disconnected) is to put ammeter inline with batt (IGN OFF!!) and monitor discharge current while disconneting various comonents..ie removing alt wires..
and as stated just cos alt is 150a dont mean batt takes x mins to charge..batt can only charge up at a certain rate, its not very efficent, and also the alt is running all electrics, so in reality its prehas only got say 50a available to charge with..8 hrs is proberly not far off..

we have a bit of a collection of cars so sometimes it can take a while for one to get used. i have installed the C-Tek plug on all our cars.. including the range rovers

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i have a c tek on my bike, fantastic chargers.

zen said:

the alt can still charge a batt but be faulty..if the rectifier pack is faulty it can put out a healthy charge but also allow the batt to drain when engine off..
one way to check, (but does require batt being disconnected) is to put ammeter inline with batt (IGN OFF!!) and monitor discharge current while disconneting various comonents..ie removing alt wires..
and as stated just cos alt is 150a dont mean batt takes x mins to charge..batt can only charge up at a certain rate, its not very efficent, and also the alt is running all electrics, so in reality its prehas only got say 50a available to charge with..8 hrs is proberly not far off..

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That is true, but on the P38, the electrical noise caused by a duff diode can also play havoc with the electronics.
I used to do a lot of sail boat electrics, an 8 hour run on the motor would bring a 150AH battery up to about 80% charge. I used to modify the alternators and fit smart regulators with 3 stage constant current charging and battery temperature monitoring that would charge the same battery to 100% in a couple of hours.

Datatek said:

It would take your alternator around 8 hours to bring the battery to 90% charged
Why waste cash on a new alternator without first checking it's at fault?
You can get overhaul kits for alternators

Click to expand...

Right bearing that in mind... I'm going to invest in a battery charger, fully charge the battery and see how it gets on.

I didn't do anything with the new battery when I got it other than put it on and use the car. Assuming that only came with a partial charge it could be that i've just never managed to actually fully charge it.