Hello to all who enter here, this truck has quite a personality, as is the nature of these rigs, apparently. Here's my deal. I bought this used in 07 w/ 135k miles, and hardly drove it till recently taking a night job. Here's the issue, after driving the few miles to work and back the truck cant hold a charge on the battery. Replaced battery w/ marathon w/ 770 CA for $109. Three days later, same problem. So I had the Marcelli Magnetti rebuilt at Tucson Alternator Exchange, and three days later, same problem. I pulled the positive cable off the battery to check the alternator. Initially it stumbled and almost died, but then the alternator picked up the spark and for the first time it had 13.5 volts across the battery posts while running. Three days later the battery is dead again, and have not been able to get the 13.5 volts to appear again. I took it out the following day to the Saguaro National Park, and it basically seems to drain the battery when gas applied, but can recharge when left to idle for about a half hour to about 11.9 volts. Any ideas of what to check next would be greatly appreciated!

 

You need to check for a parasitic current draw that is either due to an afetrmarket accessory, a short in the wiring, etc. To do that, you need an AMMETER. Typically a FLUKE multi-meter will have an ammeter function that is fused at 7 AMP 12 VDC. Disconnect the negative terminal on the battery. Hook the ammeter in SERIES between the negative battery terminal and the negative cable, do this measurement with everything turned off in the LR. You should have a reading of less than 30 milli-amps (0.030 A). Readings higher than that are a result of a drain due to the issues stated above.

 

Cheak your belt routing and belt tension, if routed wrong the alt wont charge, this is a common and easy thing that gets put back on wrong.
Also check for a loose belt, you may have a belt tensioner that is weak.

http://www.roverparts.com/TechTips/s...g_defender.cfm

 

Thanks guys for taking the time to answer my post and for trying to lead my horse to water. Thanks Unimoged, She has a trickle of drain, perhaps 1 milliamp as far as taking off the negative cable from the battery and measuring from there to the post of the battery. It is draining the battery when running, it holds the charge at rest. But I appreciate you having me confirm that right off the bat. Thanks Spike, and I immediately went out and made sure the pulley was as far back as it would go, by tightening, it doesnt appear to be slipping. But then again I dont see it when running under a load. Provided neither of these two things are the source of the problem, could this possibly be a problem with the ECM? No fault codes, just a doubt in my mind that it could have been disabled? to pick up the idle when charging? Thanks in advance for any further pearls of wisdom you might have!
Meanwhile, I got a battery charger and a spare battery and I am a gonna make it thru this one way or another...

 

Spike,
when you say
you may have a belt tensioner that is weak
do you think it would be a good idea to replace the one i have?
Regards,
charlieb

 

Did you check the belt routing? If the belt is not on correctly it will not spin the alternator fast enough to charge the battery.

No dont replace the belt tensioner unless it is weak, check to make sure the belt it tight, if it is then your tensioner is good and you have something else going on.
Always start with the simple stuid free/cheap stuff before moving on to deeper messier things.
Also check for loose wires oin the back of the alternator.
Have you checked the voltage of the alternator at idle? Should be 13-14 volts with no load.