O/T battery life

Nancy Howell · Jan 26, 2011

My truck (97 F350 7.3 diesel) has 2 975 CCA batteries. Had them checked in Oct. to make sure they were in good shape. Both are at 100%.

With the engine off (no power from alternator) how long would these batteries last with a constant 2 amp draw in moderate temps (say 50 degrees outside) before they got too low to start the truck?

2x4 · Jan 27, 2011

at least 8 hours. Friend forgot headlights on bright all day, once.

Anonymous-0 · Jan 27, 2011

What's the draw from? If it's for something that will run the battery down on a regular basis, a deep cycle battery is better designed for this. Dave

UncleTom · Jan 27, 2011

2 amp is a lot really, im guessing a day and they would be dead.

Anonymous-0 · Jan 27, 2011

Sure there is some monkey math to give you almost the exact answer but 2 amps is quite a bit I think. Do you know what the draw is? Is it something you HAVE to have constantly on or can it be switched off? Don't know about the amps draw, but I left the lights on (all except headlights) from Friday morning til Monday evening in my car once and it still spun right over.

Dave

VADAVE · Jan 27, 2011

Oh about 2 weeks.

36 Coupe · Jan 27, 2011

My wifes 85 chevy had a bad trunk lite switch that kept the lite on.Day to day it was ok but needed a boost if it sat over the weekend.That bulb was a 1 amp drain at most.My wife went to visit her mother over a week end.Wouldnt start so her brother put a new battery in the car.Same trouble.I was haying so told her to have it checkd at a garage in the town she worked in.Mechanic put on a new alternator.Same trouble.No start when parked for 2 days.This was getting expensive.Got my meter and opened the hood and took the bulb out of the hood lite.Disconnect the battery and find a 1 amp drain.I open the trunk and touch the bulb with my finger,its hotter than a fire cracker.Its been on full time for about 2 weeks, that when the problem started.The chevy parts man said , thats a common problem .Disconnect the battery, let the bulb cool and take it out of the socket.New switch cost 4 bucks.Cost 200 bucks to fix a 4.00 problem.You truck has 2 batteries so it might last longer also new models has some full time current drains that can run batteries down.

Anonymous-0 · Jan 27, 2011

That 975 CCA is Cold Cranking Amps not AH, Amp Hours. In order to convert to AH you need to divide that number by 20. 975/20 = 48.75 AH. Since there are two batteries theoretically you have 97.5 AH of power. So divide the 97.5 AH by the 2 AMP draw and you have 48.75 hours of use at a 2 amp draw. These lead acid batteries do not discharge at a linear rate so your results will not quite equal the calculated results.
STARTING BATTERIES are not deep-cycle worthy. So, you can only have the first 20% of that CCA/20 figure without damaging that battery.

Nancy Howell · Jan 27, 2011

Question relates to my horse trailer. Thinking about going on a trail ride where the camp doesn't have any electrical hook-ups. That means the interior lites in the living quarters and the water pump would run off the deep cycle battery on the trailer.

If you leave the trailer lights hooked up to the truck, there is a 2 amp trickle charge to the deep cycle battery on the trailer. The guy who installed the living quarters warned me about leaving the trailer lights hooked up to the truck because the 2 amp draw to the trailer can pull your truck battery(s) down.

My thought was to hook up the trailer lights to the truck only as an additional source when I needed it to make sure the deep cycle battery didn't get too low. Maybe 6-8 hrs over the course of two days. Could also crank the truck and let it run for a while so the alternator could charge the truck batteries.

Just want to make sure I don't pull the batteries down on the truck. Last thing I want is to try to jump start a diesel.

onefarmer · Jan 27, 2011

Why not test it at home before you go away? Leave it to run down for 24 hrs see if truck starts ok then try 36 and then 48. Just have a battery charger close at hand.

Goose · Jan 27, 2011

Those sneakies get interesting.

One of my wife's brothers brought a full sized Chevy conversion van to my shop with the same problem, the battery was down every few days. He'd had it to two shops in his hometown and both struck out.

I verified with an amp meter that there was a draw on the battery, just about enough to wiggle the needle on the meter. I checked the obvious stuff and couldn't find anything so I started pulling fuses. When I pulled the fuse for the horns and interior lights, the draw went away. All the lights were turning off like they were supposed to, either with their own switch or with the door jamb switch.

I looked at the horns, and both were unplugged at the horns themselves under the hood. Touched the wire to one and it tooted. I pulled the steering wheel and found the horn button had broken and shorted. What had happened, was the horns had stuck and my BIL unplugged them at the horns. This left the horn relay still energized, which was what was draining the battery. I fixed the horn button, plugged the horns back in, and no more problem.

Whyizzit that people never tell you the whole story? Must have been a heckuva horn relay to survive being energized for a month and still work like it should.

Sorry, Nancy. Didn't mean to hijack your thread.

Kentb of SWMO · Jan 27, 2011

Nancy,

Install a Battery Isolator on the truck. Then install a battery on the trailer that is charged through the trailers umbilical and the battery isolator. Then you can COMPLETELY dis-charge the trailer battery without affecting the charge of the truck's starting batteries. This is standard camper/RV trailer wiring.

Kent

Allan in NE · Jan 27, 2011

Yep,

Unhook the electrical to the truck until you need to charge the deep-cycle.

When it gets low, hook back up and idle the truck to recharge. That diesel will idle for an hour on half a gallon of fuel.

Don't forget to unhook it again. :>)

Allan

Allan in NE · Jan 27, 2011

Yep,

Unhook the electrical to the truck until you need to charge the deep-cycle.

When it gets low, hook back up and idle the truck to recharge. That diesel will idle for an hour on half a gallon of fuel.

Don't forget to unhook it again. :>)

Allan

John A. · Jan 27, 2011

Nancy, I have been running a pickup with 2 batteries since the early 80s, when I was Irrigating on the High Plains, Would have to be able to pull up to a Irrigation well, Big DSL Tractor, or Semi, No matter the temperature and bust it off with no help from anyone else. So two Batts were a necessity. I just replace one of mine on my 01 F350, DSL late fall, I thought I had a Glow plug, or Glow plug Relay go bad It was just the LH Batt dieing. Your pickup shouldn't loose much charge as long as you are running it pretty regular, 1 or 2 / week, If you go longer there is where things get tricky.
It might be that one of the Batts have started taking a nose dive since you had them checked. Possibly! or you have a drain that you are not aware of.
A permanently mounted Waterproof Battery Tender might be just the ticket to keep everything in order.
I hope this helps! IMO there is nothing more aggravating than Battery trouble, Y'all take care!
Later,
John A.

JDemaris · Jan 27, 2011

Depends on the specific battery. CCA has nothing to do with it. You have to look at the RC (reserve capacity) or AH (amp hour) specs.

The best batteries I know of, for your truck have 150 minutes of RC.

At a 2 amps draw, one battery will be dead in 31 hours.

So, with two batteries, it will be around 60 hours, i.e. around 5 days.

Note that if you do that, you will ruin the batteries pretty quick. They are not built to be that deeply discharged and live full lives.

For your horse trailer, you ought to have separte deep cycle batteries - hooked to a relay so your truck charges them when driving.

One pair of 6 volt Trojan T-105s - hooked in series - will give you 225 amp hours at 12 volts. That will give you 2 amps for over 100 hours - i.e. over four days.

sotxbill · Jan 27, 2011

Is this from the safety battery on the trailer charging or some other device?

buickanddeere · Jan 27, 2011

Batteries have to be replaced in a matched set. The same age, CCA, AH and should be the same make/model.
Miss matched batteries in parallel will discharge each other.
Miss matched batteries in series will eventually cause cell reversal on the weakest battery. Explosions from the rapid production of H2 gas are common.

NEKS · Jan 27, 2011

Had a 92 ton chevy and the dome light button on the door would let the dome light come on. It seems they mounted the button on the side of the plastic dash and when the truck set in the sun the button would bow the dash and the dome light would come on. Took about three weeks to find. If you drove it every day you never new you had a problem.

Sid · Jan 27, 2011

"So, with two batteries, it will be around 60 hours, i.e. around 5 days."

I for one like the fact you addressed the question but around here a days is 24 hours.

Sid · Jan 27, 2011

And "a days is" should be typed "a day is"

JDemaris · Jan 27, 2011

Do you have some sort of PMS problem? Or do you represent the new "word police?"

Notice I qualified my statements with "around" and did not say exactly how many days.

As to my spelling and grammar? I type answers fast, with a lot of arthritis in my fingers.

I do so in an effort to get my general point across.

I am not writing a Master's thesis, nor am I sitting for a Doctoral Dissertation. Been there and done that many years ago. Not required here.

Sid · Jan 27, 2011

NO I do not have PMS. NO I do not represent the word police.

Yes I noticed you said "around". 60 hours is way short of five days. A person could have gotten in trouble if they counted on about five days when they had less than three.

AS to the spelling and grammar, I was pointing out my mistake in my original reply. I made no refference to your spelling or grammar.

As to getting your point across, You do a good
job of addressing the question and avoiding a lot of trivia that has nothing to do with the question.

Sorry I did not mean to offend.

Mike (WA) · Jan 27, 2011

Math calculations notwithstanding, we find we need to re-charge at least every other day, when using the camper on the truck. I don't think the truck batteries are isolated correctly- should look into that!

Allan has the answer- Keep the trailer unplugged, then plug it in and start the truck to recharge at least every other day, preferably every day. Much better to recharge too often- to avoid "that sinking feeling" when you turn the key and get rrr. . . .rrr. . . .rrr.

Its especially annoying if you're the last one to leave camp. Wife had to flag down someone once, when horse camped in the mountains.

Actually, jump-starting a diesel is not a big problem, if you have decent (rough translation: Expensive) jumper cables, and the donor vehicle is running at fast idle.

JMS/.MN · Jan 27, 2011

Our pickup camper gets its power through a cord that plugs into the trailer hookup on the rear bumper. Plugged in during the day, it charges the camper battery, unplug at nite, camper feeds off the battery, without drawing down the engine battery.

old · Jan 27, 2011

To tell the truth one can not say and be 100% sure. Why there are just plain to many variables to figure in. A person could try a test on say 100 pairs of batteries and you would probably come up with 50 different out comes. Ya there are ways to figure it out if and only if every thing is just perfect. Ya I know but me I do not live in a perfect world but JD probably has it as close as it can be figured

teddy52food · Jan 27, 2011

I tend to disagree with you when you say mismatched batteries will discharge each other in paralell. I have a 78 ford pickup that I used to boost other nonstarting vehicles including the township road grader. I had 2, 12 volt batteries hooked in paralell. They were anything I had as a spare & most were mismatched in size and age,& they were ok until one got a dead cell , then they would both go dead.
Also, what do you mean when you say that mismatched batteries in series will cause reversal on the weak battery? Please explain as I have never heard of that before. Thanks.

DoubleR · Jan 27, 2011

I learned my lesson the hard way years ago. Like the others say, just unhook the plug to the truck. When the batt. gets down some just plug it in and run the truck to charge it. Myself, I carry a small 2000 watt invertor with a charger to just as a additional backup to the backup. I can also use the invertor and just forget about the batts. It guiet enough and most people by me don't even know its running.

JDemaris · Jan 27, 2011

Mixing different versions, or different aged batteries can certainly cause problems - but not always. It's all about the battery nominal voltage. That varies with age and make. When one battery is higher then the other, it sends current to the other as they try to become the same voltage.

Sometimes it's minor issue that goes unnoticed and sometimes it's a big one. Much depends on how big the voltage difference is.

This pops up often in big battery banks. If you've got a $3000 battery bank, and after one year - one battery goes defective . . . you are not going to buy all new batteries. You try to get one that has near the same nominal voltage, that's all.

O/T battery life

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Similar threads