My experience with the last 3 Ford diesels I have owned has supported the practice of changing them both at the same time. After a series of changing one battery every 3 months for about a year, I finally ended that trend by replacing both. This is advice consistent with many of the "long time" posters on this site and others - including a few techs. It doesen't happen right away, but clearly a weak battery will cause the good battery to work harder. This produces more heat and will reduce its life.

 

I agree if you have a weak battery replace it, if you don't why replace it.

 

The key point is - Most of the time when one fails, the other has already had to work harder and is already weakening (and you do not know it).

If I had two new batteries and one failed within a month or two, I probably would load test the other and keep it ...... if it tested good. On the other hand, after 3 years (probably even after 2 years) and one goes bad - they both get changed. Saves a TON of headaches (again personal experience).

 

same here...

 

Have no issue with .... Get it tested etc.... But just to assume everytime a battery goes bad ..... buy two. Sorry, My advice is to get both tested if one comes back good etc.....

 

I guess you are just lucky. I have seen countless issues where only one battery was replaced and then the other battery dies a few months down the road and in the process kills the new battery. You'll be playing the swap game a lot more often. This method had been proven time and time again. Same thing goes with a failing alternator, once you've realised it it's usually too late and you need to replace both batteries or you will kill the new alternator.

 

Funny. I just finished quite an experience with this...

On my 03' (orginal batteries), one wasn't charging as well as the other for some reason (both had water)and since I'm cheap, I only replaced one. For about 3-4 months if I let the truck sit longer than a week, the truck would be dead. I'd jump start it, and let the alternator do most of the re-charging while driving (was towing the RV on camp trips like everyother weekend and the RV does not have a battery on it right now...it was stolen...different story). I admit I re-charged like this at least half a dozen times. Anyway, last week while at the dealer they mentioned that both batteries had about had it...I figured that they just wanted to make a sell as one was almost new. That night we left for a trip. About an hour into the drive while towing (trailer lights too and all), the dash battery/charging system light came on...we were towing uphill pretty much in the middle of no where. 30min later ALL electrical on the truck died. Gauges, all lights (on the trailer too), etc. Everything. We ended-up making it to the nearest town and had to spend the night in a Walmart parking lot (instead of on the coast). Next moring I had to replace both batteries (w/ Walmart 65 Series) AND had to find a parts dealer that had a alternator in stock on a Saturday. Out of only three stores in that town, ONE had it in stock. Bought it and installed in on the side of HWY 1. The wife was NOT happy, the kids where freaking-out, and I was STRESSED...DEFINITY learned my lesson on that trip.

 

I still stand by what I said..... Have them both checked..... I have replaced many batteries in the 23 plus vehicles in our unit, well not me personnaly but my guys, and Most probally in a couple of instances one battery went bad and some time later the other went bad but that was it ..... I do not remember a single time that a third batt in the same vehicle went bad

 

EOD Guy - do not so quickly dismiss the specific experiences of diesel truck owners. Your experiences seem to be "indirect". You stand strongly behind your opinion, but have not built a case on why it is applicable to personal diesel truck ownership. Who knows - maybe there are specific differences in your fleet experience that do not apply to personal diesel truck ownership.

A specific "technical" reference to the practice of replacing batteries together is below:
Pacific Power Batteries - About Automotive Batteries
Go to the end of Section 7.2. It states:
"When connecting in series or parallel and to prevent recharging problems, do NOT mix old and new batteries or ones with different types"

I guess a person can always say this is hype from a battery supplier, but it is one more source of reference.

 

Interstate - 1,000 cold cranking amps. Need that here in WV in the WInter. A pair of them was $180.00 with my discount.

 

Shopping around and looking to buy batteries next week...

The Interstate battery replacement is 850 cold cranking amps????

 

Change both batteries.

And 'no'......I'm not a 'source'.......

Autocraft 'silvers'. Advance Auto Parts. Got 'em 3 years ago and still going strong.

I WOULD, however, recommend routinely checking the water in the batteries....making sure the terminals are free of corrosion, and applying anti-corrosion spray to the terminals, or else over time, the batteries have trouble even receiving a charge. For damned sure do this if you have the truck anywhere near salt and spray....and don't try to do truck PM when you are ALREADY out in the wildnerness on the Outer Banks---and you don't have all of your tools with you.....

I mean, I'D never do something dumb like that.....It was someone else! I swear!!!

p.s. At the time (2005), I paid $139 for the pair. Good bargain IMMHO.

 

They are wired in paralel in the SuperDuties.

 

Yes, I meant to correct that post earlier but forgot to in my reply. Series would create 24 volts and half the amps.

 

Deka all the way!