Why Dead Batteries?

[Unforgiven]

I didn't start the the truck last weekend. But since there is no digital radio/clock, ecu, or other obvious drain on the system I was not concerned.

Today I went out to crank it and the batteries were dead. What in the world is connected to these trucks that makes the batteries drain so quickly?

There's really nothing that I can see that should have made the batteries drain within two weeks. Obviously I will put a cutoff switch on it now that I realize it drains like this. But I would like to isolate the culprit.

 

[mckeeranger]

I didn't start the the truck last weekend. But since there is no digital radio/clock, ecu, or other obvious drain on the system I was not concerned.

Today I went out to crank it and the batteries were dead. What in the world is connected to these trucks that makes the batteries drain so quickly?

There's really nothing that I can see that should have made the batteries drain within two weeks. Obviously I will put a cutoff switch on it now that I realize it drains like this. But I would like to isolate the culprit.

It sounds like there is a problem with your truck specifically. Our trucks can sit un-started for weeks and still have strong batteries. M35 and M817.

With charged batteries, take off a cable and put an amp meter on it to see how much you're losing. Maybe knowing the rate of flow will give you an idea where to start troubleshooting.

 

[Carl_in_NH]

It is unquestionably your truck and not all trucks; you need to start troubleshooting to isolate the issue. My two M35's go for weeks without any discharge issue.

You might also have soft batteries that can't hold a charge for any length of time (self discharge). You can test for this easily enough - just disconnect one battery terminaly and wait - see if they remain charged after a couple weeks by reconnecting the terminal and trying to start it.

 

[G-Force]

You can also do it with a test light with a 24 volt bulb in it. Put it in between the battery post and the cable end with charged batteries. If it lights you have a current draw. Then go around and disconnect positive leads until the light goes out. The wire that makes the light go out is the one that has the draw. I would start with the alternator first.

 

[dittle]

Like the other guys have said, you have something up with your truck. Either a small battery drain or weak batteries. Cheap and easy way of working around the battery drain is to get a battery disconnect and put on your Negative battery post.

 

[Field Artillery]

If you have the new style push button light switch, start your search there. I had one that went bad and drained batteries. These switches are poorly designed and have flimsy electrical contacts.

You'll need to attempt to isolate the problem by disconnecting every suspect source of your ground/short (e.g. starter solenoid) and test the battery for for current flow after the disconnect. Also look for worn positive wires grounding themselves.

 

[glcaines]

If you have a hot-water heater installed, make sure that it is turned off since it is powered separately from the master. The wiring diagram for a Deuce is very simple and it is very easy to troubleshoot. What everyone else has said is true. You should not have problems leaving your Deuce for weeks or possibly even months, unless you have faulty batteries or something draining your batteries.

 

[DieselBob]

I remember reading a post on here awhile back that indicated a bad diode in the alternator can cause this.

 

[blackwater1]

Check to make sure your dash lights are not on another thing that may cause the bat drain is a bad diode in the charging system

 

[emr]

ALSO... Your batts may have been just holding enough charge to keep up and just went down, they may have a bad cell, they may be sulphated and not holding a deep charge, A batt discharges every second, to a small degree for sure, but none the less the more longer they sit for times not used they sulphate, only a fully charged batt can sit for 4 days before measurable sulphation occurs, Now I hear U saying it ran 2 weeks ago, are these new batts , if so were they charged sll the way up, and if they are older do U know there history, they may have been left unattended for months at a time then only jumped to run a short distance, that kills batt life, Are u drive enough highway distance to charge em up full, or are all your trips short and the batts are getting lower and lower untill this happens, It may very well could be an alternator and these trucks are known for that to happen now and again, but not so many as to blame the alts, remember how many trucks are out there, and how much they are neglected in the ways I stated, U need a good battery/charger/maintainer/desulphator, and should remove the batts and clean em and charge em up full individually 1 or 2 times a year, and rotate em too, the lower charge rate like 2 amps will charge a batt closest to fully charged, a 15 amp will only get it close, because if a 15 amp charger would charge to a full charge, it would actually over charge the batts, that is why a slow long charge is deeper and better. just some batt info, since this is maybe a batt problem......

 

[Keith_J]

I remember reading a post on here awhile back that indicated a bad diode in the alternator can cause this.

Exactly. Which is why you need to disconnect the big battery lead and do the test light procedure.

 

[Unforgiven]

Thanks for the info. The batteries are not even 2 years old. But I rarely used them. They were in a Suburban mounted for RV purposes like camping. They weren't exposed to harsh conditions but maybe they can't keep the charge. I'm surprised because Interstate batteries are usually pretty reliable. I have another pair of smaller batteries that I can swap in. If they go down then I'll know it's something in the truck. I was just wondering if this was a common problem. Apparently not, based on the replies. I will definitely put a neg. side cutoff switch.

 

[tm america]

do you have any 12volt taps off of your first battery . if so that is probably your problem. it will make the second bettery overcharge making the battery unable to hold a charge. . i disconnected my 12volt tap and there is no problem with my batteries holding a charge now.

 

[chiefwollam]

The simplest is the light switch, if you are not careful, you can go into the blackout drive marker mode without realizing it until..... guess what, the batts are dead. Been there, done that....

 

[Irv]

A common problem with these rigs is the starter switch becoming slightly conductive over time. What happens is every time you hit the starter, high current flows into the starter, which is operated by inductive electromagnets spinning around and interacting with the stationary electromagnets. You have stored magnetic energy, the same as in an ignition coil. When you release the button, just as in a set of points, that magnetic energy collapses and reintroduces a very high voltage across the starter button. There is a solenoid in between, now that I think about it. Same principle. The magnetic field in the starter solenoid collapses and introduces the very high voltage across the starter button and hence, the little spark. That spark is comprised of metal vapor that deposits on the normally nonconductive plastic walls of the starter button. You also see this phenomenon in light bulbs, where they get dark over time. It's metal deposition. That metal is conductive and provides a weak path to ground, thereby draining the battery.
If you do a test with an ammeter, you can tell if you have something draining the battery or if it is internal battery conduction, and time for a new battery. With nothing on in the truck, put a digital multimeter between the battery and the hot lead (or the ground side. Same answer, either way). In theory, you should see no current. In practice, you will see some milliamps. If you see lots of current, there's something draining the battery. A drain of an amp would kill off a car battery in around 100 hours, if it had a capacity of 100 AH, as a wild guess. If you have a drain of a half amp (500 mA), the battery would go dead in 200 hours, and so on. The capacity is not the same as cold cranking amps. That is a much higher number.
If you just put a battery switch inline, you will solve two problems; one being the dead batteries, and the other problem being the danger of some yayhoo at a public display climbing in the cab and hitting the starter, and running someone over. Just disable the truck with the switch. This switch will not suffer the same problem, because you will be turning it off without any magnetic energy stored. Irv

 

[MWMULES]

The simplest is the light switch, if you are not careful, you can go into the blackout drive marker mode without realizing it until..... guess what, the batts are dead. Been there, done that....

Just spent a few hours this weekend helping a buddy trouble shoot the same problem. Turned out his light switch was on blackout marker!

 

[littlebob]

All good ideas, I would take the batteries and have them checked. My useful life experience in BATTERIES is they usually last me 2-3 yrs before they start giving me trouble. After two years ,(with car batteries) I usually leave something on and they never fully recover from a total discharge with simple non computerized charger.

 

[derby]

Just curious, Would a bad Solargizer cause this?

 

[Unforgiven]

Wow! You guys have brought up stuff that I would have never even considered. Thanks.

Yes, I have a 12 v center tap right now. But it's going bye-bye soon. Yes the starter looks really old. I've never heard of that metal deposit phenomenon but it makes sense. No, the light switch is not in blackout but yes, it is old. Yes the batteries were allowed to drain (after I sold the Suburban they sat in the garage for a year). I topped them off with H2O and they charged fine.

What wonderful suggestions. I'm going to investigate all of them when the weather breaks. Right now it's cold, windy, and rainy. I don't have the space for an indoor garage big enough for the truck. I'll post pics in a few weeks of my wiper upgrade w/different battery system. Now I'm definitely putting a negative terminal cutoff on the batteries.

 

[roscoe]

My heater fan will run with the master switch shut off. Its easy to miss on a cold day.