Battery Type for Dual-Battery 1HDT?

[Dork]

Just to add my recent learnings. I bought a pair of Odyssey 34/34r to put in my hdj81. Was doing work to my truck over a span of far too long, and left them connected which ended up draining them pretty horribly. After some repair cycles with the charger, they both lose voltage while just sitting on the bench, but one at a MUCH faster rate than the other.

They would have been in parallel the whole time, so it seems to me that you can't count on batteries being identical long term. Or something.

 

[mudgudgeon]

Just to add my recent learnings. I bought a pair of Odyssey 34/34r to put in my hdj81. Was doing work to my truck over a span of far too long, and left them connected which ended up draining them pretty horribly. After some repair cycles with the charger, they both lose voltage while just sitting on the bench, but one at a MUCH faster rate than the other.

They would have been in parallel the whole time, so it seems to me that you can't count on batteries being identical long term. Or something.

Batteries don't like to be left sitting.

I've lost a couple of expensive batteries the same way. Very frustrating.

 

[duece71]

Looks like I should change BOTH batteries at the same time when the time comes. This is a good thread.

 

[jellis]

I finally got a chance to check voltages, and it's weird.

With everything disconnected on the LH battery including the alternator, my alternator will output 14.8V. If I reconnect the fusible link on that side and disconnect the alternator (so now all electronic circuits are connected between both batteries, but no charge input from the alternator), the alternator now outputs 14.35-14.4V. This does NOT change, ever, regardless of what's happening with the 7.5A Charge fuse even if no fuse is in there at all.

The fuse does not seem to control alternator output voltage but instead seems to control nominal ambient voltage to the rest of the truck. With no fuse in there (open circuit), I get 13.45V on the + terminal and 12.9V on the - terminal of the fuse. With a normal fuse in there, both sides drop to 12.93V. With my GM diode, + 13.25V and - 12.9V. With a huge 22MOhm resistor or 3 1N914 diodes in series, it acts as if there's an open circuit and goes up to + 13.45V and - 12.9V. So as resistance goes up across the terminals the voltage does go up, but it has no affect on my alternator output voltage whatsoever.

So, I'm not sure what to think. Basically the option which yields the greatest voltage increase is simply to leave the fuse empty. Is something wrong with the regulator on my alternator or what?!?

I thought I would update this thread with additional info in case this happens to someone else. In the process of chasing nightmarish dash light issues for a few days, I discovered a few things and learned even more. For one, my L wire terminal on my alternator does not have continuity to ground and therefore my voltage regulator is bad (even though it's an expensive TT alternator only a few years old, bummer!). The Charge fuse circuit ends at the L terminal on the alternator, so I could say "that would explain why my voltage wasn't adjusting with the diode" as I detailed above. However it's not clear to my why this works at all in the first place because the L wire is intended to be an OUTPUT of the alternator not an INPUT.
I don't think this diode in the Charge fuse is a good approach. Especially on our diesel trucks, that Charge fuse circuit is a wild bizarre thing and replacing the fuse with a diode is not advised. For one, it's a fused circuit and we're making it an unfused circuit. For two, there are other systems that tie into that circuit such as the pre-heat timer. For three, it's not clear how or why putting a diode in the L line affects alternator output voltage at all. The alternator should be relying on the S (Sense) terminal to determine output voltage. In fact, that is the entire purpose of that line into the alternator. So, why the hell are we unfusing a fused circuit and screwing with a line that's actually an alternator output (L wire) instead of adjusting the input line (S wire) that is specifically intended to input ambient voltage for alternator voltage regulator adjustment of output voltage?

I need to redo my alternator connector anyway because my wires are frayed, and when I do I'll be putting a diode in line with the S line on that connector and I'll be leaving my Charge fuse in place as designed.

 

[ikarus]

Question for the battery gurus. The batteries in my HDJ81 (stock 24v starter) are the correct 27/27F combo and seemingly identical.. except one CCA is 810 and the other 710. It's been working fine for the past year and a half, through cold winters as well.

Do CCAs need to match precisely in this battery orientation? Maybe in the long run, the 710 will fail slightly earlier than the 810 and bring them both down?

Doesn't seem like an urgent problem but I would be curious to hear everyone's opinions

 

[Dilspec]

I’m not sure it matters but I run matching batteries.

 

[IanB]

I think it does matter, but I'm not the guy to provide the scientific explanation as to why. If it was me, I'd go with the lower CCA rating to get a matching pair.

 

[jellis]

I am not a battery expert by any means, but here's my $0.02.
The important thing about batteries is that they are both equally functional, I think. By that I mean that you want two new batteries not one old one and a new one. This is because if one is old and cannot reach max charge capacity, or self-discharges quickly, it will constantly be draining the good one when the car is off. Basically, my understanding is that they'll always be sort of fighting each other. A bit like replacing only 1 of the 4 batteries in your flashlight or whatever.
CCA is a very specific measure using a very specific test with insanely high amp loads. I don't see having these two numbers match on the two batteries being relevant to overall battery longevity, personally. I believe that CCA has a lot to do with battery construction (plate thickness, spacing, etc.). Reserve Capacity is probably more interesting as that indirectly relates to how long it would take a battery to charge, and a differential in charging times between the batteries could lead to them having different voltages when the car is turned off and then "fighting" as described above.
I'm 2.5 years into running 27M and 31 Odysseys with wildly different CCAs & Reserve Capacity because I wanted to max capacity: not having my batteries die in the middle of nowhere while running my fridge was WAY more important to me than having them last a long time. Worth noting: This is about as much life as I've managed to get out of two different sets of normal lead acid batteries which did match. These Odyssey's still seem great (it would be interesting to measure actual capacity now, is there a charger that can do this for car batteries?). In fact, my alternator has been going out for months and just died on a 2-hour drive home up the Burr Trail from Lake Powell and these topped off quite quickly once on the charger at home.

FWIW, I had a master toyota tech buddy tell me that vibration is the #1 killer of batteries in a properly maintained system, I guess it's really hard on the plates?

 

[ikarus]

I am not a battery expert by any means, but here's my $0.02.
The important thing about batteries is that they are both equally functional, I think. By that I mean that you want two new batteries not one old one and a new one. This is because if one is old and cannot reach max charge capacity, or self-discharges quickly, it will constantly be draining the good one when the car is off. Basically, my understanding is that they'll always be sort of fighting each other. A bit like replacing only 1 of the 4 batteries in your flashlight or whatever.
CCA is a very specific measure using a very specific test with insanely high amp loads. I don't see having these two numbers match on the two batteries being relevant to overall battery longevity, personally. I believe that CCA has a lot to do with battery construction (plate thickness, spacing, etc.). Reserve Capacity is probably more interesting as that indirectly relates to how long it would take a battery to charge, and a differential in charging times between the batteries could lead to them having different voltages when the car is turned off and then "fighting" as described above.
I'm 2.5 years into running 27M and 31 Odysseys with wildly different CCAs & Reserve Capacity because I wanted to max capacity: not having my batteries die in the middle of nowhere while running my fridge was WAY more important to me than having them last a long time. Worth noting: This is about as much life as I've managed to get out of two different sets of normal lead acid batteries which did match. These Odyssey's still seem great (it would be interesting to measure actual capacity now, is there a charger that can do this for car batteries?). In fact, my alternator has been going out for months and just died on a 2-hour drive home up the Burr Trail from Lake Powell and these topped off quite quickly once on the charger at home.

FWIW, I had a master toyota tech buddy tell me that vibration is the #1 killer of batteries in a properly maintained system, I guess it's really hard on the plates?

Interesting, good to know. So are you still using a 24v starter?

 

[jellis]

Absolutely, I go to Wyoming in winter to visit my wife's family where it can be -20. It routinely hits single digits at my house (7500'). I've thought about converting, but basically everyone I've seen that does the conversion lives in a temperate climate. A new OEM 12/24 solenoid is like $250, if you're real worried about failure that's pretty cheap insurance--but I haven't replaced mine yet, or my starter. Also, you can do the @Squash mod and create a switched bypass for 12v start on the 24v starter.

 

[TheBussman]

many of the mismatched battery trucks that came in have a large leak in one of the batteries. I think that one of them will get overcharged and boil if that are not matched. some of these caused alot of damage, much more expensive then what matching batteries would cost.

 

[duece71]

I was told that mismatched CCA batteries will cause problems. I went with the same CCA for both. Batteries plus, Duracell.

 

[veiloctane]

YepView attachment 3069349

I love this the weight is amazing. Time to ditch my AGMs and upgrade to these.

Would 4 6S packs be over kill?