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#4672588 - 02/20/18 11:05 PM F-350 Batteries - What Not To Do
tom slick Offline


Registered: 05/26/03
Posts: 9308
Loc: Central Coast, Calif.
We have a small fleet of vehicles at work with forklifts, trucks, and tractors. The guy in charge of maintenance ( as an additional duty) takes care of them like his own; in over his head, being cheap with repair parts, and cobbling things together.
Today I was asked (again) to use “my” battery tester. I purchased a tester for the company that walks you the test sequence but I still get asked if I can test them. I asked what the problem was and was told “I’ve had to jump start the F-350 (2013 Powerstroke) for the past few mornings but it starts fine all day. I changed the battery not that long ago and the terminals look good, I can’t figure it out”. I go out to the running truck and can smell a battery boiling. He had changed one battery awhile back but the other was the original. Now both batteries are bad. Being cheap and changing only one battery in the end cost more.

This same guy has changed a starter because the forklift wouldn’t start, then changed the battery because it was dead, then realized the alternator belt was loose. It squealing for weeks was never a clue.
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#4672591 - 02/20/18 11:13 PM Re: F-350 Batteries - What Not To Do [Re: tom slick]
Linctex Offline


Registered: 12/31/16
Posts: 6186
Loc: Waco, TX
Originally Posted By: tom slick
He had changed one battery awhile back but the other was the original. Now both batteries are bad. Being cheap and changing only one battery in the end cost more.


Ironically....

I swapped the Cummins into my F250 in summer 2007, and had one Group 78 MAXX-1 that was (near new) given to me, but it was dead. It charged up just fine.... so I went to walmart and got another exactly like it (albeit 7 mos newer) and swapped the pair into my truck.

The pair lasted until summer 2015.... 8 years. Go figure.

I guess even a broken clock shows the right time twice a day........
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#4672740 - 02/21/18 07:06 AM Re: F-350 Batteries - What Not To Do [Re: tom slick]
2015_PSD Offline


Registered: 09/26/10
Posts: 7356
Loc: SE Texas
My 2015 had to have both batteries changed under warranty in less than a year because the positive posts on both were leaking acid and starting to corrode the cables. So far, so good on the replacements, but like yourself, I would never change just one of them--even on my own dime.
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#4672792 - 02/21/18 08:15 AM Re: F-350 Batteries - What Not To Do [Re: tom slick]
motor_oil_madman Offline


Registered: 11/29/09
Posts: 4894
Loc: Houston, Texas
Had this problem on my truck. One battery dies then pulls the other one down when it's off resulting in a no start.


Edited by motor_oil_madman (02/21/18 08:15 AM)
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#4672802 - 02/21/18 08:21 AM Re: F-350 Batteries - What Not To Do [Re: tom slick]
Blkstanger Online   content


Registered: 08/13/11
Posts: 1974
Loc: Lakeside, CA
A coworker of mine just had a battery die on his Ford F-250. He took it to a shop and they told him that they recommend replacing both for this reason.
Common problem on these duel battery systems.
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#4672886 - 02/21/18 09:13 AM Re: F-350 Batteries - What Not To Do [Re: tom slick]
pcoxe Offline


Registered: 05/14/07
Posts: 446
Loc: South Carolina
When charging batteries in series, the one with the higher internal resistance will receive a higher voltage than the other. Older batteries have higher resistance. Matched batteries will receive an equal charge. Easiest way to match batteries is for both to be new.

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#4672921 - 02/21/18 09:42 AM Re: F-350 Batteries - What Not To Do [Re: tom slick]
CT8 Offline


Registered: 10/09/14
Posts: 11239
Loc: Idaho
My wife has a 2002 7.3 and the batteries never make 3 years and one battery will be bad and the other will boil. I change them ever 2.5 years as a prophylatic. I remember one morning when my wife was leaving hearing the engine missing really bad in the drive way and thinking oh nooooooooo . I took a couple of deep breaths and checked the batteries and one was bad, I put 2 new batteries in and the truck ran like new. I don't know how the new engines run with marginal batteries.
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#4672930 - 02/21/18 09:46 AM Re: F-350 Batteries - What Not To Do [Re: Linctex]
CT8 Offline


Registered: 10/09/14
Posts: 11239
Loc: Idaho
The 6 inline Cummins sure as a better feel that the V8.
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#4672943 - 02/21/18 09:52 AM Re: F-350 Batteries - What Not To Do [Re: pcoxe]
brianl703 Offline


Registered: 05/07/04
Posts: 10597
Loc: Nokesville, VA
Originally Posted By: pcoxe
When charging batteries in series, the one with the higher internal resistance will receive a higher voltage than the other. Older batteries have higher resistance. Matched batteries will receive an equal charge. Easiest way to match batteries is for both to be new.


So the F-350 has a 24 volt electrical system?

You learn something new every day.

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#4674375 - 02/22/18 12:24 PM Re: F-350 Batteries - What Not To Do [Re: tom slick]
Papa Bear Offline


Registered: 08/11/05
Posts: 7073
Loc: Leamington, ON, Canada ..... r...
2 batteries in parallel 12V, not 2 batteries in series 24v
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#4676311 - 02/24/18 10:11 AM Re: F-350 Batteries - What Not To Do [Re: tom slick]
George7941 Offline


Registered: 05/10/05
Posts: 2164
Loc: Toronto, Canada
I have to go against the combined wisdom of all the contributors to this thread and state that while it is optimal to have matched batteries, it is really not as critical as many many folks make it out to be. Especially with the older dumber charging systems which did not sense charging current but only regulated voltage, they just limited charging voltage to 14.4V or thereabouts. With that kind of system, you could have a truck battery, size 31, and a motorcycle battery, 10AH, in parallel and neither battery is going to get overcharged.

With current sensing charging systems, yes, it can be an issue because, depending on the mode of failure of one of the two batteries, it could be drawing excessive current, leading the charging system into thinking that the batteries are discharged and raising the charging voltage beyond what is optimal.
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#4677063 - 02/24/18 10:05 PM Re: F-350 Batteries - What Not To Do [Re: tom slick]
brianl703 Offline


Registered: 05/07/04
Posts: 10597
Loc: Nokesville, VA
It's far more critical to have a matched set of batteries if they are in series.

As we've established that the F-350 has the batteries in parallel, it doesn't matter quite as much, so long as one of the batteries doesn't have some kind of internal fault (like a shorted cell) that will cause it to drain the other battery.

If one of the batteries has just lost capacity, that really doesn't matter for a parallel battery connection.

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#4677179 - 02/25/18 01:32 AM Re: F-350 Batteries - What Not To Do [Re: brianl703]
George7941 Offline


Registered: 05/10/05
Posts: 2164
Loc: Toronto, Canada
My thoughts, exactly. As you can see from most of the replies to this thread, a majority think that parallel batteries must be matched. Not necessarily!
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2006 GMC Sierra 4.3l, NV3500,G80 , Mobil 1 5W30, Dexcool.
1987 BMW R80 - sold
2015 Honda CBR300R

Staying out of the right lane a lot.

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#4680212 - 02/28/18 03:06 AM Re: F-350 Batteries - What Not To Do [Re: George7941]
DoubleWasp Offline


Registered: 05/21/12
Posts: 5293
Loc: Fort Lauderdale, FL
Originally Posted By: George7941
I have to go against the combined wisdom of all the contributors to this thread and state that while it is optimal to have matched batteries, it is really not as critical as many many folks make it out to be. Especially with the older dumber charging systems which did not sense charging current but only regulated voltage, they just limited charging voltage to 14.4V or thereabouts. With that kind of system, you could have a truck battery, size 31, and a motorcycle battery, 10AH, in parallel and neither battery is going to get overcharged.

With current sensing charging systems, yes, it can be an issue because, depending on the mode of failure of one of the two batteries, it could be drawing excessive current, leading the charging system into thinking that the batteries are discharged and raising the charging voltage beyond what is optimal.


There's one thing you are missing here. The way they like to do these things is to have the alternator sense from one battery (connected straight to vehicle electrical) and charge the other one (at the end of the combining charge cable), with the charge coming back through the combiner to the sense battery. This is how the "one dead, one boiling" happens. Mismatch the batteries, and the S will hit the fan faster.

When the system only senses and charges one battery, it's almost worse. The second battery just gets whatever the primary battery requires, regardless of what's really going on there.

This is why in the marine business, boats with multiple batteries generally use combiners and isolators. Either a regular dumb alternator charges into a box that doles the power out completely independently to each battery's needs, or a dumb alternators send its charge toward the main battery, and then the combiner cable has a box spliced into the center of it that doles out the power as prescribed for the secondary battery.

With either method, any battery can do whatever it wants without affecting the others, since they are isolated.

With either method, you can hook a wire to the starter's signal circuit that will combine all batteries for starting, and then isolate them once starting is complete.

With the second method, an indicator light is mounted to the dash that shows when the secondary battery's charging is going on. If the light is on too much, you know there is a problem.

The first method is definitely preferable.
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