Rotate batteries???

[Mark Rinker]

As I changed out another set of ~3 year old Delcos recently, it occured to me that my fleet maintenance has gotten lax recently when it comes to battery 'rotation'.

Back in the 6.5L days, it was common practice because it seemed we were forever cleaning terminals, inspecting grounds, etc. to keep the cold blooded beasts starting through the winter. We would regularly swap the location of the dual batteries, ensuring that if one had been isolated due to a bad connection or ground, it would now be in position for the next round of abuse...and the battery that had been starting the truck solo would be in for equal duty, or eventually respite - if the same connection problem were to re-occur over time.

Since both batteries were mounted up front on the 6.5s, not much thought was given to the environment each lived in, it was connections and grounds as the variable...enter the unique locations of Duramax dual batteries in 2001...with one mounted up front near the drivers side headlight bucket (a cooler environment) and the other that lives back against the firewall soaked in underhood heat from engine and the nearby turbo.

After replacing three pairs (2001HD, 2002HD, 2006K3500) of OEM Delco batteries in as many years on the Duramaxes, I have noticed that 100% of the time its the passenger side firewall battery (same one that pukes out the vent in the summer time) that fails.

My new theory is if I rotated batteries each fall,each set would last at least one season longer...or reduce battery replacement costs on the fleet by ~30%. A hidden advantage is by rotating, you are also cleaning and treating terminals to dielectric grease.

Time is money.

[More Power]

Interesting thought about battery location and failure rates. The factory batteries come with an insulation wrap. Would probably be a good idea to continue using them when new batteries are installed. :)

Jim

[trbankii]

I'm a little late to the 6.5 game, but have been having various thoughts along these lines about the batteries myself.

Various people liken electrical circuits to plumbing so that you can "see" what is going on - switches are valves, wires are pipes, etc...

My analogy of the dual battery setup is of two barrels and two pumps. The first barrel is the driver's side battery. The first pump sends the water from the first barrel over to the second barrel - the passenger side battery. The second pump takes the water from the second barrel and feeds it to the starter motor (ok, so I'm mixing items in my analogy).

This is all well and fine as long as enough water gets to the second barrel to keep the second pump supplied. But any restriction in the water flow and the second pump starts sucking air when the second barrel isn't getting enough water to keep it filled - corrosion on the terminals, low battery charge, voltage drop in the wires, etc - and the passenger side components seem to get the greater abuse.

Initially I was thinking of an isolator system of some sort because I was figuring that the batteries were getting out of balance and then causing parasitic drain. But it seems to end up being more that the passenger side battery ends up working harder and getting overheated more often due to parasitic losses between the two batteries - if that makes any sense.

Experience with big rigs and heavy equipment with multiple batteries never seemed to have the same level of problems - but one difference is that in those situations the batteries are always sitting right next to each other with short connections between them. I know that GM has the underhood setup for supposed ease of maintenance, but would it help to have a battery box under the bed to get the batteries closer together without the underhood heat?

Just trying to think out loud here on some of these issues...

[Mark Rinker]

Hmmm...interesting analogy and observations. You might be on to something.

There is definately energy loss from the 6.5L driver's side battery to passenger side battery to starter, especially with OEM cabling and any corrosion or aging at the connections, terminals, and grounds. Replacing the + cable that runs from side to side over the top of the radiator with larger diameter (lower gauge #) and better connectors will help alot. Same for ground/starter cabling and all connections...

I have no doubt that relocating both 6.5L batteries elsewhere, and side by side would eliminate that loss. The closer to the starter, the better...my C4500 has both batteries located under the passenger step area, close together AND closer to the starter...not by chance, I am sure!

But, we digress...this IS a Duramax forum, and cabling isn't a problem there, in the light duty series anyway. However, keeping the passenger side bat-tree cooler in the summer heat (especially when towing, which is CONSTANT in our world...) is!

Hmmm...maybe there is a trick modification or cool product needed here? Or maybe just a set of Optima Red Tops... :)

[Mark Rinker]

Interesting thought about battery location and failure rates. The factory batteries come with an insulation wrap. Would probably be a good idea to continue using them when new batteries are installed. :)

Jim

EXPERIMENT #1: Put a coozy around a beer, and put it next to your battery on the passenger side firewall. Place another beer next to that one, without a coozy. Drive 300 miles in July with 12,000# of steel in tow behind you, averaging 62mph with the A/C on high. Stop and measure the temperature of the beer in both cans.

EXPERIMENT #2: Tape a thermcouple attached to an electronic thermometer to the top of each battery, in between the battery posts. Drive 300 miles in July with the same 12,000# of steel in tow behind you, averaging same speed, etc...etc... Record the temperature at each battery. Which one is hotter? How much hotter?

EXPERIMENT #3: Remove the wrap from the batteries and repeat experiment#2. What changes?

(If you have ever ridden behind a Duramax in the summer with no heat shield (C4500 with doghouse removed, looking for a noise) - and only pulling its own weight - you have a pretty good idea of the answers above. The underhood heat is incredible. So hot you can't stay in the cab long, even with the windows down.)

A1: Both beers are as hot as the ambient underhood temperature.
A2: The firewall mounted battery nearest the turbo is much hotter than the battery mounted behind the headlight.
A3: The batteries heat up faster, but both arrive at the same temperatures as Experiment #2.


The insulating wrap probably helps us the most in Minnesota by retaining heat from the previous day's run (and charging) as overnight temps draw heat from the truck until it matches the ambient outside temperature. As for shielding heat, it should probably be wrapped in heat reflective material like the firewall if its purpose is to reject heat...even then I think in short order it would fail to make a difference.

[tufcj]

I have an 03 K2500HD. Batteries are both original as far as I know. I bought the truck used in 2004 with 26K miles (from my brother-in-law). I noticed that one battery is 600CCA and the other is 700CCA. I don't remember which is where. Was it normal to have 2 different rated batteries?

Bob
tufcj

[Mark Rinker]

Nope. Are they both AC/Delcos?

[trbankii]

Another piece to my analogy - that the alternator connects up to the driver's side battery. So not only is the starter motor "pumping" from the passenger side battery and draining it harder due to "restrictions" between the two batteries, but "filling it up" again runs into those same restrictions going the other way...

[tufcj]

Nope. Are they both AC/Delcos?


Yep. Both AC/Delcos. Talked to my BIL, and he doesn't recall having either changed. He bought the truck new.

Guess as long as they work, I'll just leave them and replace both when the time comes.

Bob
tufcj

[JohnC]

If both batteries share the load equally (worst case) then the current on the cable between the two is half the total starter draw. If the cable size is the same as the cable feeding the starter then the resistance of the cable between the batteries is insignificant and for all practical purposes the batteries are equally loaded. (How's that for circular logic? ;) )

The alternator charging current is small compared to the starter draw, and if split between the two equally, half of small on the interconnecting cable, and also not significant, IMHO.

[trbankii]

John, that does make sense explained out that way.

Just from gut instinct it seems that the passenger side battery isn't getting much love and trying to mentally sort out what is going on in order to improve the situation.

And my posts should probably be deleted from this thread and moved over to a similar thread in the 6.5 forum. When I first posted I came in from the "new posts" link and wasn't really considering that the 2500HD/3500 forum was under the Duramax section. If you want me to, I'll copy and paste them into a new thread so that you can delete these posts.

[Mark Rinker]

I don't see any problem discussing 6.5L battery cabling compared to the Duramax setup at all. Thanks for your input!