I've had this truck a couple of months. One battery looks new one old. I've had it in the shop with the AC several times since I had it. When I put it in the shop, the batteries run down from cranking and not running long, I guess.

So I was thinking of replacing the older battery when the AC mechanic told me I should replace both batteries at one time even if one is fairly new.

Is this just a good idea for folks with several hundred dollars to throw at once or is it really necessary?

I would just get another identical to the newest one. Matched batteries is a good idea.:)

Repeat after me: "Always replace batteries in pairs..." That's the best way to do it. If one battery is stronger than the other, it will always try to discharge and bring the other one up to snuff. It's a good practice to have matched batteries. Some people will even try to match the lot numbers or manufacturing dates. I just try to buy a new pair whenever I need them, which isn't often. I just put in a pair of Optimas and hope to get a lot of years out of them.

Jake

You change your socks in pairs, don't you???:p:

New batteries will pay for their selves also. Less drain on alternator + better fuel economy & less wear on alternator.

Yes, internal resistances will differ between batteries over time. Meaning, one's gonna pull more for charging than the other one, and one's gonna give more during glow time and starting too. Balanced set WITH good cables AND good connections. Bad connections will be worse than mismatched set of batteries depending upon how poor the connection is.

DP, do how far out do you take the decimal on the fuel economy?

That's why I never use the cig. lighter: poor mileage.:smoke2:

I'm going to start driving with my lights off, since wasting electrical power hurts gas mileage.






>>>
I bet I get smacked down for that comment.

All in good fun--- gotta go, left my dome light on.

GAS mileage????

But I replaced mine in pairs and let me tell you, my truck was like a rocket after that..... you'll be able to tell a difference between old and new batteries!!!

I have those eveready MAXX ones and I replace mine under warranty for free about once every 7 or 8 months (on my 2nd set).....

Gas mileage? Socks? Rocket? You guys pulling my leg?

Load is load so I guess some mileage gain to be had ( I would like to see a Mythbusters episode tho on just how much gain, sort of along tailgate up vs down lines).

Replace in pairs always otherwise older battery when paired eventually acts very similar to a dead cell in a battery, and can also kill the newer battery.

Hmnn takes off like a rocket with new batts (that one requires further study), maybe some sort of low voltage causing low performance of fuel driver, low lift pump flow, partially opening shut off solenoid causing IP flow restriction, that one is hard to convince myself there was an improvement, but if it made a percieved difference to the operator then "what the hey".

Bottom line best practice is replace in pairs, & I'm one of the anal guys that goes thru the stack of batts looking for 2 from same mfg lot/batch

DP, do how far out do you take the decimal on the fuel economy?

Should say economy in general. Less alternator wear, less underhood temps, battery life, and fuel economy is a plus. I am currently going to underdrive my alternator to reduce load there, since my truck is a highway use vehicle.

When I can stabilize my driving habbits I go to the hundredths. :)

Removing the bug deflector (mileage deflector) I picked up .3 miles to the gallon.

Fabricating a true ram air system 1.1 mpg

Exhaust is next

Silverado 4.8 Extended cab:

Stock 18.7 mpg
Modified 21.1 mpg currently

Well I say like a rocket, because when I did replace them the old batteries wouldnt even turn my truck over, so they were just dead beyond charging, I had the alternator checked and they said it worked fine and the batteries just went bad, so it was just something that went over time probably since the day I bought it.... so the performance of all the electronics was lower, and with the new batteries I could feel it had gotten snappier throttle, better low end and just all around more performance, even better fuel mileage....

I bought my truck with one brand new expensive battery in it and one old battery. I couldn't justify buying a new epensive matching battery so for the last 6 years i just replaced the batterys one at a time as they go bad. I say myth busted. Put in one at a time unless you have 2 identical batteries to start with and they are both quite a few years old. Me I'll never buy two new batteries for my truck. Old ones I put in last years. I may put a new one in the wies car and put her old battery in the truck. If you have one bad cell out of 12 it will drag the rest down some but I don't really think you need two batteries. Now the battery dealer will tell you different.

Where do you hail from Stump much cold weather where you are at, low batts really show ugliness when it turns cold, having to buy 1 new batt every year did I read that rite ???

I don't run the mega $$$ battery 5 yr warranty Walmart or Autozone or other in pairs has worked well for me, $150 for the pair IIRC 6 years ago on the Truck, only into year 2 on the pair in the Burb, as far as myth busting $75/yr (avg cost 1 good batt) x 6 yrs is what $450 over the same time period spent for a $150 pair, that is $300 difference that could be put to something else ( say a $30 100 amp load cell battery checker for instance); or did I misunderstand your scenario.

Also consider what else mite go bad as result of low voltage until you get around to checking batts remember some of this stuff on the 6.5 really does not thrive on low voltage. IE stuff like DP points out

If you run one good battery and one not so good, your alternator will be working full time, all the time. The weak battery will pull down the new battery overnite and then the next day, quess what? Charge both batteries while your driving the next day.

Where do you hail from Stump much cold weather where you are at, low batts really show ugliness when it turns cold, having to buy 1 new batt every year did I read that rite ???

I live in Colorado but the truck stays in the garage. I plug it up to the wall if I use it in the cold. I only installed 3 old batteries in 5 years. I installed used old batteries each time because my vehicles have a pecking order for who gets the best. My rock crawler jeep gets the brand new Yellow top Optima. The wife car gets a new battery or the best battery I own besides the yellow top. The tractor is family so it will get a good battery out of the truck and then my poor old truck. If it was my baby I'd slap 2 red top optimas in it and put huge battery cables on it. With Optimas you would need a trickle charger to keep them up if you don't use them everyday. So I think every bodys right hear. If you want the best then buy 2 new batteries and call it good. If you are afraid to install just one battery then don't be. Ive done it for years and have seen it done in marine applications many times with no harm done. If you do have one go bad then the other battery will get drained enough that your rig won't start and if you keep charging the dead batteries to keep them going then yes you will harm the other "good" battery. Moral is that just because it has two doesn't mean that one can be bad.

I'm sold. I'll be replacing both batteries and I'll hold the newer one of the two in the Burb for whatever needs one next with a spare battery tender - just sold one of my old collector cars.

Power of suggestion anyone???:cookoo:

Sorry, that was in reply to; nosmoke97.

After a few weeks of dragging at startup (I did check my cables and grounds) I finally stranded myself at the gun club :o:.

Turn the key and not even a grunt from the starter. My glow plug light wouldn't come on and the buzzer (door open) sounded sick.

A friend showed up and we tried jumper cables. Put them on the pass side battery and nothing changed. Put them on the drivers side battery and the glow light came on and I'd get a weak little grunt from the starter.

Another friend showed up and we put each of thier trucks on each of my batteries with cables. Still just a weak engine turnover and no start.

Finally yanked the batteries (CarQuest April 2005 900cca) and headed for Sams Club. One tested at 10.5v the other at 12.2v, but I figured they'd be tired anyway and they didn't load test them...I think thier tester is just a voltage tester that calculates available amps based on tested voltage (which seems bogus since they don't charge them and put them under load).

But anyway...I bought 2 Sams batteries - they are only like 630cca (at 32deg) but they are what the book showed. $58 each with 3 year replacement and 8 year pro-rate. So I'm gonna give 'em a shot and see how they do.

They sure spun it over FAST:eek: compared to my startups over the past several months. There was an engine knock for the first few seconds after startup - could there have been an excess of unburnt fuel in the system from all my attempts to crank the thing?

All is well and $58 each for a couple of batts w/ 3 year full replacement is pretty good. No reason to buy just one at that price!

I don't have cold weather to contend with or I might be more concerned about the CCA.

BTW, is the starter 12v or 24v? It appears the batts are wired in parallel for 12v and I expected it to be in series for 24v?

Also, the batteries each checked 12.4v the other day at the house, but I didn't disconnect them and wonder if I was just getting the 'average' voltage? Guess they need to be disconnected to actually check thier individual voltage? What's the proper way to check voltage on dual batts?

Also, what is the best way to check alternator output? Can I do it w/ a standard voltage meter?

Thanks!

Chaser

12 volt starter, dual batteries help out with the 21 to 1 compression and also the glow plugs can pull the voltage down quickly, especially on a cold day. Check battery voltage separately and the alternator should be putting about 14.5 volts.

I know from experience that both batteries have to be good. I spent months trying to track down what I thought was a micro-short that would drain my batteries over a week if the truck was left sitting. Turned out one old battery was draining the one good battery until both were dead. To make things worse the constant draining ruined my new battery. I don't go to the extreme of matched lot numbers, or even matching manufacturers, but I do make sure I have two batteries of similar age with the same amp hours. However, if you CAN buy the same batteries at the same time then do so.

I strongly disagree with the fellow that just buys a new battery when one fails. The weak battery will destroy your good battery much faster than if you had two good ones. It's false economy.

630ccamps? Sounds a bit light.....

To check alt output, you'll need an amperage clamp meter. One that does DC amperage (most do AC, you'll have to make sure that the meter you select does DC). Test it right at the post coming off of the alternator. The nice thing about the clamp meter is that you can test various items on the electrical system to see what their draws are.

So I should check the alt AMP output? Not the alt VOLT output?

What amperage should I be looking for? What is a good source for the DC amperage clamp?

Thanks,

Chaser

Voltage is the normal test for alternator output and if it is putting out the right voltage then it is probably putting out amps, but if batteries are charged it not going to show large amperage. There are ways to have the alternator put out the max amperage for test purposes but you would need the service manual to no how. Amp meter is an excellant tool for checking draw of components eg. starter, glow plugs.

Finally yanked the batteries (CarQuest April 2005 900cca) and headed for Sams Club. One tested at 10.5v the other at 12.2v, but I figured they'd be tired anyway and they didn't load test them...I think thier tester is just a voltage tester that calculates available amps based on tested voltage (which seems bogus since they don't charge them and put them under load).


Also, the batteries each checked 12.4v the other day at the house, but I didn't disconnect them and wonder if I was just getting the 'average' voltage? Guess they need to be disconnected to actually check thier individual voltage? What's the proper way to check voltage on dual batts?

Also, what is the best way to check alternator output? Can I do it w/ a standard voltage meter?

Thanks!

Chaser

10 and 12.2 are technically DEAD batterys they cannot be load tested at that voltage, minimun to load test is 12.6V

if you checked your batterys and they tested 12.4 with the key off/all assy's off. your alternator is NOT charging and your running off battery voltage, fully charged batts after sitting should show 12.8V it will be higher if tested shortly after veh is shut off, charging voltage can range from 13-14.75V any higher and the alt is full fielding and over time will boil the batterys

So I can just take my meter and check DC volts at the alternator post at idle, fast idle, etc... to check the output, yes?

My dash volt meter says I'm charging at basically 13.5v-14v depending on if I'm running day or night. But I'd like to verify it at the alternator w/ a meter unless that's unnecessary.

Thanks for the really good info.

As an aside, my Land Cruisers alway had AMP meters. You could see how hard the alternator was working, but you didn't know the voltage. Kind of odd... They'd really peg out when you hit the winch button!

Chaser

Yes check your voltage at the alternator nut AND at the batterys they should be the same... have you removed or replaced the battery spacer in the pass side positive battery terminal yet?

Yes check your voltage at the alternator nut AND at the batterys they should be the same... have you removed or replaced the battery spacer in the pass side positive battery terminal yet?

12.56v at the batts non-running.

14.46v at the ALT post at idle. 14.41v at the drivers battery, 14.40v at the passengers battery.

Battery spacer looks like new as do all the terminal posts.

The truck cold cranks in almost exactly one second. It's doing fantastic.

Thanks,

Chaser

Okay, quick flash on electrical stuff here....

There's a difference between amperage (current) and volts.

Think of it like plumbing. Current (amperage) is like how many gallons of water you are moving. Voltage is the amount of pressure in the line. Two distinct measurements of different qualities.

You can have plenty of voltage, which is a good indicator of you have sufficient generating capacity. The alt will "throttle" itself as to not put out excessive electrical current and run the voltage up so high to cook the batteries. However, voltage will not tell you how much current you are actually using.

Some shallow well pumps can put out x-amount of water, and you can only get your shower with it and maintain pressure. If you turn on the dishwasher, hot tub, lawn sprinkler, washing machine and dishwasher at the same time, your pressure goes down quickly, because the amount of water required is so large that the pressure goes to nothing because of the resistance to flow in the size of the plumbing pipes, and the capacity of the pump.

Now, a deep well submerisble pump can deliever far more gallons of water at a higher pressure than the pump above. You may even have enough pumping capacity to run the whole list of things above and have pressure.

Measuring the current with a DC clamp on meter will tell you how much current is moving through that section of cable/wire. Between the alternator and the rest of the truck electrical system will tell you how much it's putting out. Watch the number change as you "load up" your system with turning on more and more devices.

Checking each cable to the batteries will also tell you a story as well. If they are both accepting a charge, or if they are charging unevenly. If they are charging unevenly, then you may have some dis-similaities between batteries internally, or the quality of the connections and cabling.

Volts is only part of the equation. Current is the other portion. There's watts too, but that's a whole 'nother thread there.....

I picked up a DC clamp on meter from that auction site for cheap. It was only for quick diagnosis stuff on the bus... didn't really need to make a sizable investment for "everyday usage." Check the specifications before purchasing one that it will do "DC" amperage. Most do AC, only a few do DC.

I have had my truck for 6 years now I had to replace the batterys the first year and now I need new ones again
The one thing I have noticed with my truck is that there is no maintenance or repair that is cheap exept maybe an oil change if you cant afford 2 batterys how do you keep your truck on the road

For those that notice that their batteries don't seem to do as well as say a passenger car battery, there are a few considerations:

Truck batteries (diesel applications) require large amounts of current to start the engine and glow plugs.
High CCA battery's plates are very tightly spaced in the cells. This reduces the "margin of error" for shorting a cell. Less plates per cell, the lower the cranking amp rating.

My K1500 came with one AC Delco (unknown age) and one Econo Power Premium USED battery. Talk about oxymoron, I didn't think you could use premium and used same sentence when talking about a battery.

Anyway, I replaced them both today with new MAXX-78N batteries from Sprawlmart. It was the only way I could afford to replace both at the same time, but at least the truck is running now. When it was 85+ degrees out no problem, but we had a cold spell a week ago and we're just getting through it now and I tried to start it two days ago without success. I tried again today after checking the glow plug circuit and it still didn't want to go. Now it starts without a hitch.

For those that notice that their batteries don't seem to do as well as say a passenger car battery, there are a few considerations:

Truck batteries (diesel applications) require large amounts of current to start the engine and glow plugs.
High CCA battery's plates are very tightly spaced in the cells. This reduces the "margin of error" for shorting a cell. Less plates per cell, the lower the cranking amp rating.

Excellent point. I always used 625CCA batteries (4) in my Mack and they would last 5+ yrs. Other people insisted on 900CCA and they never seemed to last more than 2-3 yrs. I thought that I once read that in a given size battery (dimensionally), a higher rated battery would have more, thinner and more closely spaced plates. You just confirmed that.

Now if you just had enough real-estate available for three instead of two batteries..... I had to buy Optimas last year to fit in my slide out battery tray... couldn't find a lead acid battery available retail to fit. I think that that Delaware Transit must had a vendor that would provide special sized batteries that would just squeeze in or somethin'...

For those that notice that their batteries don't seem to do as well as say a passenger car battery, there are a few considerations:

Truck batteries (diesel applications) require large amounts of current to start the engine and glow plugs.
High CCA battery's plates are very tightly spaced in the cells. This reduces the "margin of error" for shorting a cell. Less plates per cell, the lower the cranking amp rating.

Do you think that one would get better longevity from their batteries if they pulled and did maintenance charges yearly, to help with plate buildup?

I'm not much of a lead (acid) head..... so there's a lot of learning still for me to do under the "battery" heading.... Describe maint. charging. I saw a feature on a battery charger at Stuff*mart about adding life to your battery somehow....

IMO, THE BEST maint. for a battery is to check water level every 6 months or so and top up with distilled water, AND keep your batteries clean.

I wish I had a picture (but I don't) of me with a voltmeter probing the battery case. You will actually get a voltage reading inches from the terminals if your batteries are dirty.:eek:

Keep them clean, keep them topped up, and if not being used for extended periods, keep them charged.

NEVER leave a dead battery in the winter, charge it ASAP. When a battery is low on charge, it can freeze. When it freezes, the plates can bend and touch and junk the battery.

The quickest way to kill a battery is to continually discharge it. Keep them in good condition, clean, charged, and expect long life.

I'm not much of a lead (acid) head..... so there's a lot of learning still for me to do under the "battery" heading.... Describe maint. charging. I saw a feature on a battery charger at Stuff*mart about adding life to your battery somehow....

The only thing I know about batteries is that the vehicle charging system does nothing for accumulation on the battery plates, whereas a standard battery charger will remove the "stuff" (don't remember what it's called) from battery plates.

By maint. charge I mean pulling the battery (or both) and putting it on a charger at a low 2 amp charge for a period of time. Additionally, I check the water level and clean the case and contacts.

I've used some additive I got from Harbor Fright because a friend recommended it highly. I don't know whether it actually does improve the battery or not. Fortunately the product wasn't made by the same supplier as the automotive fuses!