I am experiencing something similar - battery drops almost 0.1V per day whether or not the truck is being used. However it doesn't seem to be a bad alternator nor a bad battery..... but it has to be, right?

Truck is a 1999 RAM 2500 V10 4x4 XLT (manual)

0) Truck is used exclusively for 11 minute drives (6 miles), two per day, every other day or so. RPMs are usually 1200-1700 (it's a 5-speed V10, I can drive it at idle)

1) At all RPMs the voltage (there is 0.04V drop from alternator to battery) is above 14.3V, in fact it stays tightly in 14.3-14.5 range. (I have a digital voltmeter hooked up at all times)

2) On a more or less charged battery (I plug it in and charge it at least once a week), at idle, the alternator is putting about 0.4A-0.8A into the battery. (Amp meter in series). If I drain the battery a little (headlights for 1 min), it initially dumps 10A in but this quickly comes down to less than 1A again (about 1-2 minutes).

3) Once I shut the engine off, the voltage gradually drops (as expected for surface charge) back to what it was before I started it, about 2-6 hours.

4) Driving longer distances does not seem to increase battery voltage outside of the surface charge as mentioned in #3

5) Battery is new, old one had the same symptoms but was more abused and more dead (previous owner). Old one was a Bosch, this one is an Everstart MAXX (oversize - 1000A, barely fits).

6) Parasitic drains vary from 100mA-150mA. Maybe they get lower after a few hours, I never checked. This seems high, but they are evenly distributed across several fuses and I was not able to isolate it to anything specific or reduce it any further (It was 500mA+ when I got it due the infamous defective seat belt control module). This is the XLT so it has all sorts of so-called luxury trinkets that could be sucking up current.

Nonetheless, 150mAh is 3.6A per day, which should not be that much to a battery with (I'm guessing) over 100A useful capacity (so it must be bad?)

7) I've added a 5W solar panel on the roof in a desperate attempt to offset the drains and maintain battery. I sadly miscalculated the charging needs (300mA in full sun = about 15mA on average, especially in winter) The solar panel does not drain anything when it's dark (checked).

8) Despite what's been mentioned in this thread, I've pulled the battery on a running truck and there was no change in system behavior or voltage - and this really does suggest to me that the alternator must be fine (and the system voltage never drops regardless of loads - even high beams+fog lights). Could it still be a bad alternator?

9) I am particularly concerned about the battery appearing to have very low capacity - that is how I'm interpreting its tendency to shoot up to 14.5V immediately after I start the car. Two bad batteries? Or is the truck killing them somehow?

10) The truck has a battery temperature sensor underneath the battery (in the tray) which from what I can tell is used to control the charge level to avoid overheating(?) the battery. I have the shop manual (>3000 pages) but it doesn't have any info on verifying its proper operation, so I'm not sure if that could be a culprit.


If I can't figure this out (I'm planning to exchange the battery if I find the receipt) I was thinking of putting in a Battery Brain to disconnect the battery whenever I leave. Any experiences with going this route? I'm not sure if losing ECU memory, etc would be an issue.


Well that's a lot of info, but hopefully someone can point out a flaw in my reasoning.

 

I don't know what it is but, it's most likely something simple(99 times out of 100). You do need to drive it more. The engine never gets to operating temperature, which will lead to all kinds of problems.

 

good god that's a book

 

Every battery discharges daily, even without any parasitic drain. Driving 11 miles is not enough to replenish even the drain from starting the vehicle, especially if you are also running any high draw accessories like the A/C, heater or lights. The V10 needs a battery with at least 650 CCA, but I think if your drives were longer you would see no problem. I would hate to see the inside of your engine, though, if this type of use has been going on a long time.

 

Read the thread "pcm??????????" it is my thread and will probably help you alot! I just went throught the same thing...

 

And more than likely id say it is your voltage regulator... It is in the pcm. So ull have to bypass it with an external voltage regulator....

 

Dude, your the only guy that's ever had your problem in the history of this forum, and I still say it was the alternator. you overanalize every****ingthing. Don't mislead any body until your proven to be not full of $hit. It takes a while on here. You'll be one of the guys before you know it, but right now your just entertainment.

 

Good info. Depending on your temps and what not batteries need to get up to a good temp to recharge properly. I had this same issue due to it being -2 out for 2 weeks. Once I got the battery inside and let it warm up it took a good charge.

Also if you worried about it take the battery and the alternator to your local auto parts store and have them tested. They both will need to be removed from the vehicle to get an accurate test. That will alleviate 2 things there. It can be a short somewhere. But first drive it more to get a good charge, and take your battery and alternator to an auto parts store to have them tested.

 

I appreciate all the input. I live in NJ, temps are about 25-40F over the past few months.

On the subject of short trips, I am aware that it is an issue, though coolant temp does get to full in my driving (cardboard radiator shield helps ). I realize that it takes a little time to boil all the moisture out of the oil, but, well... that's my drive to the bus stop (and after a 1.5 hour commute I don't feel like driving around just for the heck of it at 12MPG).

As I've said though, on 30-60 minute drives the battery does not take any more charge than on my 11 minute drives. Drove 1.5 hours in the snow storm last week (slow going, higher RPMs, 4x4), and battery was at 12.1V the next morning. Of course system voltage was 14.5V the entire drive.

I don't use accessories significantly (and using/not-using lights, fan, etc does not change the actual charge rate as I mentioned, I tested that). Everything is always off and finished before I shut the engine off (lights, power windows, etc). I'd even disable the keyless entry receiver if I could - I don't have any keyfobs.

I'll see if I can get the parts bench tested and perhaps I can switch cars with my wife once a week for a longer drive (30min) ... but it's pretty clear that it won't fix the electrical problem. Though she likes driving the truck

Thanks again.

PS: I wonder if this has any relevance: My digital MPG gauge (overhead computer) always reads 6.3MPG after an engine start, and doesn't budge unless I reset it - then it reads correctly.

 

Any battery will show a lower voltage when cold. Charging voltage is also not a precise indicator of charging amperage or reserve capacity. The voltmeter on these trucks is there primarily to alert you to an electrical problem, but it does not give a full picture of your charging system. Many truckers that operate in the cold wrap their batteries in an insulating blanket to prevent problems. It shouldn't be necessary on a passenger vehicle, but the way you use your truck sounds like much of your problem.