I recently replaced one of my dual batteries, and I have dual alternators. Around 65K on the truck. Original alternators.

When I start the truck, the battery light comes on for a while. Seems like it's staying on longer than usual. On my scan gauge II I notice its in the 11.5 ish volts when the battery light is on, then after a minute/two/three, it goes up to mid 13's and battery light goes off.

I don't recall it doing this before, and it seems to be staying on longer.

Any ideas?

 

I would double check the other battery. typically it isnt a good idea to only change out one battery as the newer battery will be trained by the older one. You could easily lose a cell on the older one and cause damage to the newer one.

You are noticing the lower voltage until the amperage draw from the plugs warm up. It could be dropping lower from the lack of power from that older battery

 

Two potential problems. One is the old battery. You should always replace batteries in pairs.

But a marginal battery shouldn't cause a charge light. An alternator not charging should.

I would figure out a way to test each alternator separately. One alternator could be covering up for the other one.

Try disconnecting the 2-wire connector from one alternator and then start up the truck. You should see lower battery voltage until the glow plugs turn off, then voltage should run above 13.2. The alternator light should turn on when you do this.

Then plug that alternator back in and try it with the other one. If one alt won't produce at least 13.2 volts, then I'd remove it and take it in for individual testing.

 

10-4, that's a good idea. The battery thing, I get it, but in the first 5 years, Ford replaced the passenger batt at 2 years, then the driver at 3 years, then the passenger again just before warranty expired. Never had an issue. i'm not 100% sure I really needed to replace the one battery, however, to test them, I took out one battery and drove on a single for a while, then swapped them. The remaining one did fine, the other not so fine and was almost 4 years old, so i replaced it.

I'll try this with the alternators and see what happens. Wish I'd bought that Scan Gauge II a long time ago!! Why Ford sold an HD truck with dual batts and alternators and only an idiot light for battery is beyond comprehension.

 

before you can do aproper analysis you must ensure both baterries pas a proper load test that is half the cca rating for 15 secs the batteries must be issolated and tested individually if they both pass then you can test alts on the truck with same volt amp tester because you have a dual system you may have a simple connection problem at one of the alt besu all with one pire to check the conectors at each alternator for signs of burning any good repair facility can check both batts alt volts and amp output [max] and running starter draw volt drop with one vat tester if you want to do it yourself you must take batts to someone with a load tester capable of 400 t0 500 amp draw for 15 secs then check outputs with dvom hope this helps good luck dennis

 

sorry but something went wrong with my reply iwas trying to say you may have abad connection at one of the alternaters the post connecters at the rear of the alternaters somtimes get to hot and burn usually from a poor connection

 

That's not exactly how I'd test 'em...but I guess it works.I couldn't agree with you more, though I use an AE...it's amazing what you can do with that thing. As far as the idiot light....the same reason they designed and sold a $45k truck without a factory anti-thief system like 99% of everything else they sell; including the $16k Focus. Trust me, I've at just about everyone that I can find that has anything to do with Ford. Buyer beware with the older SD...it doesn't take much to steal one. But hey, they recovered from their fumble with the '08 (and up) model Superduties.
Are you sure about that amp draw? The factory batteries are 850CCA rated. I've never load tested mine (just put a new pair in last fall) but load testing a similar style battery at a former employer would get you 700-750amp on a resistor style load tester. To say the grids got a little warm would be an understatement

 

could be the older battery is heading south too. time to change that and check both alternators. either one or both of the alternators are going bad. hence if so, then the alternator or alternators are draining ur batteries.

 

re 400t0500 amp draw yes the only accurate lod test is to load battery to one halfof thecca rating for 15 seconds if you have a 850 ccabattery the half the cca is 425 if you run 1000 cca batts then 500amps for 15 secs also be sure batts are at least 3/4 charged before load test dennis

 

[quote=River;11005589

Wish I'd bought that Scan Gauge II a long time ago!! Why Ford sold an HD truck with dual batts and alternators and only an idiot light for battery is beyond comprehension.[/quote]




with that many batterys and alternators Its got to be Frustrating and expensive

and it may just be an idoit Light but one thing that I have noticed is that light is very accurrite. once that light starts poping on odds are something is going out soon