Hey gang....my batteries won't hold a charge much over 9v, and that means it won't start if it sits for more than a day. When driving the guage shows about 13-14v, but when not running it dips down to the ~9 range. Looking at the batteries one is clean and one appears to be leaking fluid from the top caps. Is it possible to just have one dead battery in this dual set-up or do I need to replace both? One battery does not have the date notched out, but the bad one shows that it was bought in 2002. I'd sure like to spend only $80 if its possible/safe to replace just one.

 

I wouldn,t fool around with just changing one change the two of them you will end up spending the other 80 bucks sooner than you think.

 

I had 1 bad battery and it would kill the other battery, figured it out by dissconnecting the batteries. I changed it out for one I had laying around at home and 3 weeks later the otherside went. So I just baught 2 new batteries after that. I did'nt feel bad either, they were the originals.

 

I really prefer Motorcraft. I had replaced drivers side last winter with motorcraft. The other is still the old Energizer from walmart that came in the truck, it is showing some weakness. It will replaced with same as drivers side soon. My Starter killed the drivers side one first, don't know why. After replacing starter I had not a single issue. The Energizer just doesn't show full 12+ volts anymore but it still works.

 

Take the truck to a NAPA, Autozone, Advanced, Orielley's etc. Have them check your alternator. Then diconnect both batteries and have them load test each one (by itself with the cables off). This will tell you if the alternator is working O.K. and the state of each battery. A weak battery will pull down a good one connected to it. If one battery is within specs then you can just replace the bad one. Autozone has a Gold series (65-DLG) with a 3 year free replacement warranty for about $95.

 

Don't depend on the dash gauge for this kind of diagnosis. If you're looking at it after turning the key to RUN, but the engine not running, then the glow plug are lit, and that will drop the voltage considerably. Get a voltmeter and check the voltage of each battery at its terminals.

 

I am going to eventually mount 2 gauges in truck 1 for each battery. They will give me volt status and charge status. That way I always know what condition they are in.

 

Volt readings are O.K. but amps are what charge the battery and draw them down. If you install an ampmeter it will show you how much your aternator is putting out and if the alternator fails, how much is being drawn out of the batteries. You can have a battery that reads 12.5 volts but when you put a load test on it, it will not hold the load with the amp draw. Load testing each battery seperately is the way to be 100% sure of their status.

 

So I need to install to amperage gauges?? Not knowing I had a weak battery last winter stranded me.

 

Correct, at least 60 amp and it will still max out when the glow plugs kick on and the alternator goes to full charge.

 

For those of you with a Costco in your area, they have excellent prices on batteries. I just bought a set this weekend for my rig, $75 each, and 850/1000 amp rating, 100 more amps and $45 each less expensive than the Ford dealer here. Local diesel owners have been giving them high marks so far. I'll post up if/when I have a problem with them.

 

I understand what you are saying, but in this diagnosis its the batteries and the guage is correct. I have tested via volt meter. The batteries will show 12v+ while running (guage and meter), but when shut off they immediately show ~9v. This is just enough to start the motor, but after 12 hours of sitting forget it....it will turn over about 3 times and that is it. Considering one of the batteries is 6+ years old (assuming both) I'm going with the simple fix of putting in new batteries.

 

I would also have you Starter checked. Take it off and take it to someone you trust to give you good test results.

 

Again, go have it TESTED, it's free to have it tested at a NAPA, Autozone, Advanced, etc. (batteries seperately and alternator). FYI with the truck running and the alternator charging you should be seeing around 13+ volts.

jle70 has a good point also.

 

Kind of off the original subject, but. I had read on hear a while back of someone putting a battery "Tender" on line with the heater plug in. Anybody have direction?