(Please ignore my dual duals in the title)
My son has a GMC dual battery system in his 1999 Sierra 2500. I assumed the drivers side front battery was the starter battery and the passenger firewall battery was there for excess loads etc.
Can someone elaborate just a little or just tell me I’m wrong or right?
All I know is whoever decided the single battery on the GMT900 went on the firewall and not in the tray behind the headlight better work in fast food now.
In reply to Daylan C :
My 2006 Sierra 1500 has the single battery on drivers front. That’s what made me think the dual battery 2500 (same body designation) has the front drivers battery as the starter battery but “the internet” seemed to say differently which is why I had to ask here where smart guys hang out
And if you were stranded on the side of the road with a dead battery in a dual battery truck, and you could replace just one battery, which would you need to replace?
A lot of the factory dual battery trucks just run both batteries in parallel. They do it not for separate starting / other power supply, but for more power to run glow plugs, crank large diesel, etc.
In reply to rslifkin :
That’s what I thought too but again “the internet” has me thinking I might need some more education
Shades of old MGs - a pair of 6V batteries in series behind the seats gave good 12V starting grunt,
ebonyandivory said:In reply to rslifkin :
That’s what I thought too but again “the internet” has me thinking I might need some more education
The GMT800 dual battery setups are just what rslifkin said, two identical batteries in parallel. They were an option for gas trucks (and are easy to retrofit using OEM parts if you want), but they're really intended for diesels. That starter takes a LOT of current and the glow plugs are 15 amps each (there's 8 of them), the truck won't start on just one battery.
When you replace them you always do it in pairs, and you want to find a parts store that has two batteries from the same production lot.
I've replaced them singly with no issue, but only when one battery had a freak occurence and the other was still tested great.
But, yes, truck will work the same with either battery disconnected, they are just boosting each other. (Which also means you need to disconnect one when load testing)
Mercedes are the ones who make cars with a separate starter battery mounted underhood, and a mongo accessory battery in the trunk.
I've only ever heard of parallel (found in big pickups, for redundancy and increased capacity) or series (for 24V systems, like in semis) dual batteries until now, do some have a separate "starter battery?" I have heard of people experimenting with supercaps as a "starter battery" or putting them in parallel with a small battery which otherwise couldn't run the starter, but nothing like that has made it to production AFAIK.
In reply to GameboyRMH :
99 - 01 BMW 750iL has electrically heated catalysts. So it has 2 batteries. IIRC, one starts the engine and powers the catalyst heaters, the other powers the electronics. They're normally combined with a relay when running for charging, but kept separate during the startup sequence to ensure the catalyst heaters always have enough power and that they don't brown out the other electronics.
rslifkin said:In reply to GameboyRMH :
99 - 01 BMW 750iL has electrically heated catalysts. So it has 2 batteries. IIRC, one starts the engine and powers the catalyst heaters, the other powers the electronics. They're normally combined with a relay when running for charging, but kept separate during the startup sequence to ensure the catalyst heaters always have enough power and that they don't brown out the other electronics.
How very German. :)
2004 F250 super duty diesel.
If the batteries are dead, you can jump it by hooking cables to the passenger but not the driver’s side.
I have no idea why or what that means, just know from being around one since new and having to jump it quite a few times.
I vaguely remember diesel Econolines having different size batteries. One big group65 for starting and the other a "normal" group58 or 34 for what I presume was eevrything else. But Chev as far as I can remember has always been two operating the whole system.
I have a 2000 Chevy with the 6.5L diesel, and just to confirm, it is running parallel. I'm assuming that the internet's misinformation is due to the ECU and all that is connected on the left side, whereas the starter is on the right side one, but there's just a big ol' wire running between the + terminals, so it's all the same circuit.
I can say on my diesel, I've replaced the batteries at the same time but because it's not running in series so it really is just a big old CCA thing. If one battery is weak, as long as you've still got enough CCA in the system, it's not a big deal, especially on a gasser. The diesels can be pretty brutal on batteries and starters up here in the north east.
Slippery said:2004 F250 super duty diesel.
If the batteries are dead, you can jump it by hooking cables to the passenger but not the driver’s side.
I have no idea why or what that means, just know from being around one since new and having to jump it quite a few times.
Passenger side battery is connected directly to the starter (it's on that side after all) while the driver side is daisy chained through much more cable.
At least, that makes the most sense. Have never had rhe opportunity myself.
WonkoTheSane said:I can say on my diesel, I've replaced the batteries at the same time but because it's not running in series so it really is just a big old CCA thing. If one battery is weak, as long as you've still got enough CCA in the system, it's not a big deal, especially on a gasser. The diesels can be pretty brutal on batteries and starters up here in the north east.
IIRC If one battery is weak/won't take a charge then it'll drag the system voltage down and the alternator will wind up overcharging the good one to compensate.
I'll echo what the others have said... just a parallel battery setup for more available cranking amps. Follow the red wire and you'll see it just goes from one battery to the other.
Knurled. said:Slippery said:2004 F250 super duty diesel.
If the batteries are dead, you can jump it by hooking cables to the passenger but not the driver’s side.
I have no idea why or what that means, just know from being around one since new and having to jump it quite a few times.
Passenger side battery is connected directly to the starter (it's on that side after all) while the driver side is daisy chained through much more cable.
At least, that makes the most sense. Have never had rhe opportunity myself.
Makes sense.
I know I tried to jump it a couple of times with another super duty and it would barely crank until I tried the passenger side. Then it would fire right up.
iansane said:I vaguely remember diesel Econolines having different size batteries. One big group65 for starting and the other a "normal" group58 or 34 for what I presume was eevrything else. But Chev as far as I can remember has always been two operating the whole system.
It was even simpler than that. They were a normal parallel batter setup. There was a special narrow battery on the one side because that was all that Ford could fit in that space.
Having different group size/CCA/reserve capacity didn't really matter much. Batteries is 12.5-12.6 when fully charged and 11.9 when discharged, one just discharges/charges a little faster than the other. It all levels out in the end.
codrus said:WonkoTheSane said:I can say on my diesel, I've replaced the batteries at the same time but because it's not running in series so it really is just a big old CCA thing. If one battery is weak, as long as you've still got enough CCA in the system, it's not a big deal, especially on a gasser. The diesels can be pretty brutal on batteries and starters up here in the north east.
IIRC If one battery is weak/won't take a charge then it'll drag the system voltage down and the alternator will wind up overcharging the good one to compensate.
Not really... the system voltage is defined by the regulator in the alternator and will be much higher than a battery's voltage, even when fully charged.
What happens when you have a battery that won't take a charge is the same thing that happens in a single battery system... system voltage is fine, battery just doesn't charge. (Voltage actually goes UP, or rather, the AC ripple goes up, when you have a bad battery. And the modern electronic type (Midtronics) charging system testers look at ripple... a failing battery can result in a false test failure)
If you have a single battery with a shorted cell, then that can drain the other battery as well when the engine's off.
GameboyRMH said:I've only ever heard of parallel (found in big pickups, for redundancy and increased capacity) or series (for 24V systems, like in semis) dual batteries until now, do some have a separate "starter battery?" I have heard of people experimenting with supercaps as a "starter battery" or putting them in parallel with a small battery which otherwise couldn't run the starter, but nothing like that has made it to production AFAIK.
Most modern semi’s are 12 volt.
They run multiple 12v batteries in parallel to provide the cranking amps. You can jump start them using a car, as long as you are patient.
Well, I was able to test the batteries. One was reading perfectly within spec while the other tested completely dead. He’d been having trouble if the truck sat for several days without being started and run. Now the truck has two batteries with equal (perfect) voltage and lo and behold, it starts and has no problem if it sits for a couple days.
So can I assume that the (very) dead battery was cannibalizing the good battery? I mean, 12.6v hooked to a dead one would take both batteries below their ability to function in a dual battery, parallel system right?
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