I have a 2003 Dmax with original A/C Delco batteries, and I went to start my truck Monday and the batteries were dead. I charged them up and truck started fine, so wasnt sure the batteries were actually dead or if they had been drained by something. Could not find anything that I left on. Had no starting problems again until today. Went out to start my truck this morning, and once again the batteries were dead. I am assuming I have 1 bad battery. The question I have, is should I replace both batteries, or find the bad battery, and just replace it?

Always replace the batteries in pairs or you'll just be throwing away good money if you only buy one.

Replace both, with an 03 you're about due for a new set anyhow. Good time to go down to your CAT dealer and get some truck bling.

If you have one weak battery, it will evantually cause the other battery to weaken. This will greatly shorten the life of the 1 new battery if you do it that way, and then you're in an endless cycle of replacing 1 at a time. If you have the originals in now, you're due for a change, so just bite the bullet and get both replaced.

If two horses are pulling a wagon, one will wear out and stop before the other but both are tired! Batteries are the same.

If two horses are pulling a wagon, one will wear out and stop before the other but both are tired! Batteries are the same.
Yes. Exactly. If one is shot, so is the other one - or very close.

This same theory applies to anything with multiple pieces. Cooling system is a biggie. If a rad hose blows out, don't just replace that hose, replace them all. They are all just as old and have just as many miles/hours.

Shocks. Bushings. Belts (for older models). Don't just replace one bad one, replace them all.

Maybe you need 1 more person to suggest changing both together...
ac

Maybe you need 1 more person to suggest changing both together...
ac

LOL! I'll be one more! Anything that is in pairs, and opperates in the same manner, at the same time, should be replaced in pairs. Wheel bearings, batteries, axle bearings, you get the idea.

Replace both...but do not get more AC CRAPO batteries. Get a pair of good batteries !!

Optima red-tops would be just fine. A friend has those in a 2003 Dmax and they are going strong.

LOL! I'll be one more! Anything that is in pairs, and opperates in the same manner, at the same time, should be replaced in pairs. Wheel bearings, batteries, axle bearings, you get the idea.
Not sure I agree on the wheel bearing thing. Wheel bearings can last a long time, and they are not dependent on each other. Just because one wears prematurely, I'm not going to spend and extra $200 to replace the other one that's perfectly good.

Not sure I agree on the wheel bearing thing. Wheel bearings can last a long time, and they are not dependent on each other. Just because one wears prematurely, I'm not going to spend and extra $200 to replace the other one that's perfectly good.

Can't say I blame you on that thinking! These unit-bearings are way over-priced! It's just my expirience with my trucks that (and this could just be my luck....LOL) when one of a pair goes out, the other is usually not too far behind. As was the case for me with my wheel bearings a few weeks back. one was trashed, and the other was on its way out the door...and besides that, I have OCD about things like that...:rolleyes:

I have had mixed luck with Optima batteries. Some times you get some that are good, sometimes you get some that are junk. I run a yellow top in my Landcruiser, i have drained it alot and have always got it to take a charge. I will not be replacing my Duramax batteries with Optimas though. I will look for something better.

As far as your battery drainage problem, I'd bet it's your glow plug heater going bad. If you're under 5yr/100,000 miles it's covered under the emissions warranty.

Ok, I have replaced both batteries in my truck. I had both batteries checked just to make sure they were both bad, and sure enough, they were both bad. I replaced them with Duralast Golds. I had planed on replacing them with Interstates, but no one in area had them in stock, so had to go with the Duralasts. I have never used Duralast before, so I hope they do ok, besides, they even had a better warranty (3yr replacement/8 yr prorated) then the interstates.
I have noticed something strange since I have changed my Batteries though. Now when I start my truck the Volt meter only shows about 12 volts for a few minutes then it will go up to 14volts. My truck has always done this, but have never taken a few minutes, usually just a minute or so. What could be causing this? When I first bought the truck I noticed it and asked the dealer, they said it was the glow plugs, but why does it last longer now that I changed the batteries?

Glow plugs and intake air heater cycle (I've noticed it doing this longer now that it's cold)

Now when I start my truck the Volt meter only shows about 12 volts for a few minutes then it will go up to 14volts. My truck has always done this, but have never taken a few minutes, usually just a minute or so. What could be causing this? When I first bought the truck I noticed it and asked the dealer, they said it was the glow plugs, but why does it last longer now that I changed the batteries?
Mine does the same thing. 2008.

As long as it shows about 12 for a while, you are OK. When it goes down closer to 9 or 10 and stays for a while, start thinking about replacing both batteries.