KISS Dual Battery Upgrade (1 Viewer)

[TeCKis300]

There’s been a lot of discussion on batteries and battery systems. Here’s my attempt to offer an easy button. The task of a battery first and foremost is to offer power and reserve capacity. There’s many battery setups and systems talked about. But perhaps some of those are solving a problem that really isn’t there, or need complexity to solve a fundamental shortcoming of an architecture as laid out. Some may judge this as not sophisticated, at least from a traditional expo POV. I’d say KISS, with reduction of complexity and dependencies to be its greatest advantages. That’s ultimately cheaper, easier, more effective, and reliable than anything out there.

1) 2x lead acid batts (matched batts, buy at same time)

AGMs are not the right solution here. Flooded lead acid is what’s fundamentally compatible with the alternator/regulator and underhood temps. As large or small as you like. Deep cycle (hybrid) batts preferably. I’d say that 2x group 27s are more than most people will ever stretch when setup like this. Most may not even need 2 batteries and can get away with one larger battery with the expo options below.

2) Wire these batts in parallel to make one big bank

Wire with heavy 0/2 gauge. One big bank has advantages to maximizing usable capacity and huge current draws. It also keeps cycle depth low, prolonging usable life (lasting potentially 8+ years, unless you live in super-hot places like Arizona which kills any battery/setup). “But, house and starter batt”…. I’ll get there in the expo section.

3) Wire the vehicle to the batteries in cross fashion. Positive to (+) terminal on one battery. Negative to (–) terminal on other battery.

This is a key optimization for long battery life. Move the chassis ground to the battery on the other side. This is important to keep the batteries balanced. Otherwise, there will be voltage offsets and micro-currents causing premature wear.

That’s it. No fuss. Always charged. Maximizes the batt capacity possible for every device, with huge current capability.


Expo options

4) If one has continuous draw devices that operate after engine shut down (i.e. fridge, heavy lighting, house draws, etc.), they should be wired to a distribution point that is tied to the batt with a low voltage protection mechanism. This protects the batts and ensures starting reserves, which addresses the reason for house/starter batt setups.

5) If one wants to monitor voltage accurately in cab, add a USB cig lighter adapter with voltage readout ($10). Some even have low voltage alarm functions.

6) If one wants to support continuous draws for long parked durations, add a solar panel/charger tied directly to the bank. Something that makes enough output to support whatever particular draw. 50-100W can typically make the system last indefinitely, unless one has a particularly large draw.

7) Protection from battery bank failure. Carry a standalone lithium-ion jumper pack that typically doubles as a USB charger. It has the benefit of helping any expo friends in trouble, vs a built in battery jumper solution.

 

[Willy beamin]

Run a group 31 and a jumper pack as back up. That is KISS

 

[KLF]

Perhaps it's an "old wives tale" urban legend, but I heard or was told long ago that wiring batteries in parallel like that will eventually kill both batteries. They will never be perfectly matched, and will feed off each other until they are dead (when the engine is not running). If anything goes wrong in any cell of one of the batteries, it will short and kill the other battery.

My opinion: Having dual batteries provides a way to split the load, and gives the reserve system Fault Tolerance. Having an isolator allows the parked loads (fridge, lights, stereo, comms) to be handled by the less critical accessory battery only. If the primary starting battery fails, flip a switch to link them together, jump start yourself, and carry on.

 

[supercarrera]

There are some good dual battery write-ups in the 80s section as well. On my 80 setup I simply used a Blue Sea ML 7622 automatic charging relay to isolate the batteries. I had that setup for several years with no problems and used it a couple times to self jump-start myself when the primary battery went bad. It's one step more complicated than @TeCKis300 KISS solution but is still pretty simple.

 

[tbisaacs]

Run a group 31 and a jumper pack as back up. That is KISS

+1.

I’ve got single X2 power 27f, noco genius jumper, and a renogy voyager PWM w/100w panel. This setup keeps my fridge happy for the length of trips I take.

I do see the value in going dual at some point. Just not there yet. I don’t take super long trips, no winch, and really only camp in fair weather.

 

[tbisaacs]

There’s been a lot of discussion on batteries and battery systems. Here’s my attempt to offer an easy button. The task of a battery first and foremost is to offer power and reserve capacity. There’s many battery setups and systems talked about. But perhaps some of those are solving a problem that really isn’t there, or need complexity to solve a fundamental shortcoming of an architecture as laid out. Some may judge this as not sophisticated, at least from a traditional expo POV. I’d say KISS, with reduction of complexity and dependencies to be its greatest advantages. That’s ultimately cheaper, easier, more effective, and reliable than anything out there.

1) 2x lead acid batts (matched batts, buy at same time)

AGMs are not the right solution here. Flooded lead acid is what’s fundamentally compatible with the alternator/regulator and underhood temps. As large or small as you like. Deep cycle (hybrid) batts preferably. I’d say that 2x group 27s are more than most people will ever stretch when setup like this. Most may not even need 2 batteries and can get away with one larger battery with the expo options below.

2) Wire these batts in parallel to make one big bank

Wire with heavy 0/2 gauge. One big bank has advantages to maximizing usable capacity and huge current draws. It also keeps cycle depth low, prolonging usable life (lasting potentially 8+ years, unless you live in super-hot places like Arizona which kills any battery/setup). “But, house and starter batt”…. I’ll get there in the expo section.

3) Wire the vehicle to the batteries in cross fashion. Positive to (+) terminal on one battery. Negative to (–) terminal on other battery.

This is a key optimization for long battery life. Move the chassis ground to the battery on the other side. This is important to keep the batteries balanced. Otherwise, there will be voltage offsets and micro-currents causing premature wear.
View attachment 1853542


That’s it. No fuss. Always charged. Maximizes the batt capacity possible for every device, with huge current capability.


Expo options

4) If one has continuous draw devices that operate after engine shut down (i.e. fridge, heavy lighting, house draws, etc.), they should be wired to a distribution point that is tied to the batt with a low voltage protection mechanism. This protects the batts and ensures starting reserves, which addresses the reason for house/starter batt setups.

5) If one wants to monitor voltage accurately in cab, add a USB cig lighter adapter with voltage readout ($10). Some even have low voltage alarm functions.

6) If one wants to support continuous draws for long parked durations, add a solar panel/charger tied directly to the bank. Something that makes enough output to support whatever particular draw. 50-100W can typically make the system last indefinitely, unless one has a particularly large draw.

7) Protection from battery bank failure. Carry a standalone lithium-ion jumper pack that typically doubles as a USB charger. It has the benefit of helping any expo friends in trouble, vs a built in battery jumper solution.

What do you mean by move the chassis ground to the battery on the other side?

 

[Itsky]

Cool thread, thanks for the input. Leaning towards a single group 31 and anti-gravity lithium jumper. All I need it for is a fridge and ham radio

 

[TeCKis300]

Run a group 31 and a jumper pack as back up. That is KISS

Agreed! I acknowledged as much in point #1. In my own use, I will likely only ever need 1 battery worth of capacity. Potentially paired with some expo options.

Some do need two for their purposes. How to set them up is the point of this thread.

It's probably worthwhile to annotate just what kind of capacity were talking about. I'm generalizing, as different brands/variants/measurement methodologies produce slightly different numbers. For lead acid, ~50% of these numbers is the functional/usable capacity.

Group 27 - 90Ah (stock)
Group 31 - 115Ah (27% more capacity)
2x Grp 27 - 180Ah (100% more capacity)
2x Grp 31 - 230Ah (255% more capacity)

 

[TeCKis300]

Perhaps it's an "old wives tale" urban legend, but I heard or was told long ago that wiring batteries in parallel like that will eventually kill both batteries. They will never be perfectly matched, and will feed off each other until they are dead (when the engine is not running). If anything goes wrong in any cell of one of the batteries, it will short and kill the other battery.

My opinion: Having dual batteries provides a way to split the load, and gives the reserve system Fault Tolerance. Having an isolator allows the parked loads (fridge, lights, stereo, comms) to be handled by the less critical accessory battery only. If the primary starting battery fails, flip a switch to link them together, jump start yourself, and carry on.

There is some truth to the old wives tale. Wiring them in parallel will not kill batteries. It's done all the time for RVs, off-grid solar setups, etc. Wiring disparate batteries or wiring them wrong, will kill batteries. Hence point #3 above, to ensure equalized charging and loading.

Agreed, fault tolerance is important. Several trades to consider:
1) Internal shorts can happen. Part of the why batteries short to begin with is related to use and abuse. A typical cause to this failure mode of an internal short is due to sulfation sheds piled up under plates. That's related to deep cycling, overdrawing, and undercharging. Yet by paralleling two batteries together, they now share loads to halve the draw, and halve the cycle depth, partially mitigating some of the root cause of shorts.
2) If there is a fault, the car electrical system is likely to catch it with a CEL. Another mitigation is a usb battery monitor alarm, such that one is alerted to an issue before the faulty battery permanently harms the other.
3) Game changer today is the lithium jump battery. It was not possible in a practical manner historically to carry a compact jump battery, hence the advent of fault tolerance in dual battery setups. There is likely a good lead acid batt to go forward with too.

Case against isolation:
1) True, dual batts provide more total capacity to the overall system. But in isolating, any one device only has a single battery worth of reserve and power.
2) By creating a bank, every device has access to at least 2x the reserve. I say at least. Because current draw matters to batteries. A lower current draw (because parallel batteries split the draw) will result in functionally more usable capacity in each battery. Said another way, high current draw (i.e. winch), will utilize more % capacity than what it actually uses. This effect is known as the c-rate.
3) In high current draw situations (i.e. winch), parallel batteries surely will provide more performance, as there's more ampacity support, and less voltage drop, especially in a long pull.

 

[TeCKis300]

What do you mean by move the chassis ground to the battery on the other side?

Referring to the picture... Normal wiring in the car would have the vehicle (or load) + and - wires tied to the posts of a single battery. In order to ensure equalized draw and charge, it is important to actually wire the + and - wires to different batteries.

Easiest way to accomplish that is the move the battery to chassis ground wire, to the other side of the engine bay where the other battery is at. Hope that makes sense.

 

[indycole]

Just curious if anyone has tried fitting a Group 27 in the usual spot where folks tend to install a second battery? I thought about the "matched battery" approach but figured I'd be constrained to two Group 35s?

 

[Markuson]

Just curious if anyone has tried fitting a Group 27 in the usual spot where folks tend to install a second battery? I thought about the "matched battery" approach but figured I'd be constrained to two Group 35s?

I just recently put my older (but otherwise identical) second type 35 onto the main tray, replacing my type 31...so at the moment, I have matching odyssey type 35’s. So far, it seems to leech off the other less than before.

One of the interesting things with the IBS system is that the “charging” light often stays on after the truck is off. I believe what’s happening is it is “charging” the more drained battery from the other. This isn’t good in my thinking, because if one is super low...it spirals downward.

My Interstate type 31 AGM main has been a problematic battery. Interstate found an internal short-/or something akin to one (?)—in my first one...replaced it with this one (which is of similar manufacture date)...and it seems to exhibit a similar behavior.

I think they sell a tiny number of them...so I suspect they do small production runs. They are so obscure that even the main Interstate distribution point in San Diego has to special order them.

But anyway...now that my batteries match (35+35), I’m seeing better results, but I would rather have larger in both slots. Wondering what the largest battery size is that can squeeze into the Slee tray #2 slot is... But my battery use is much heavier than most. If I could, I’d love to have two “second” batteries in parallel...in isolation from the main. More like a battery bank on an RV...but not likely to happen. Might try it someday, as there is room in back...but that’s a long wiring run from the alternator.

But again, my use is extreme, so who knows.

For most folks, dual batteries are a pretty worry free affair. With heavy use of constant fridge, chargers, etc. it definitely gets complicated.

 

[eatSleepWoof]

I currently have a dual battery setup in my Tacoma using a BlueSea ML-ACR. In my next vehicle I will not run the same kind of setup. I will either have a completely stand-alone auxiliary battery which will be charged exclusively at home and by solar, or the same kind of portable, standalone "power box" that will also have an option to connect to the truck's charging system (via the same ML-ACR). Definitely do not want to keep a second battery under the hood, or even in the truck full time.

 

[KLF]

Can you elaborate why? Did you have problems or issues? Or just simplifying the system?

 

[eatSleepWoof]

Can you elaborate why? Did you have problems or issues? Or just simplifying the system?

No problems at all. It's just... not necessary. As much as I want to tell myself that having a fridge 24/7 in the truck has day to day benefits, it does not. It's extra weight and less room - nothing more. Same goes for the battery - more weight and less room, more complications all around.

The biggest lesson I learned from all the modifications I've made to my truck is that 95% of the fancy, trend-setting "overland" stuff is completely unnecessary for anyone that doesn't go on multiple 3-week-long trips every year.

The fridge is great, but requires a fridge slide, a dual battery system, wiring, connectors, circuit breakers, isolator, dedicated space, etc. It is cool as hell and I had fun building it, but I am not likely to do it again. A quality cooler will work perfectly fine for the type and amount of trips I do every year.

I also don't like messing with OEM electronics. Even when done right (which many people & even shops fail to do), it is a lot of complication for little (IMO) gain.

The best setup is a portable one that you can put into the truck when needed, and remove at other times. Goal Zero systems, as overpriced as they are, have the right idea. I would build something similar, but likely using a pair of 6V golf-cart batteries (in series). Super light, tons of usable amp hours, little (or no) modifications to the truck, and easily removable.

 

[tbisaacs]

Came back to say my Goal Zero 400 is worth the price. Literally plug and play.

 

[Markuson]

No problems at all. It's just... not necessary. As much as I want to tell myself that having a fridge 24/7 in the truck has day to day benefits, it does not. It's extra weight and less room - nothing more. Same goes for the battery - more weight and less room, more complications all around.

The biggest lesson I learned from all the modifications I've made to my truck is that 95% of the fancy, trend-setting "overland" stuff is completely unnecessary for anyone that doesn't go on multiple 3-week-long trips every year.

The fridge is great, but requires a fridge slide, a dual battery system, wiring, connectors, circuit breakers, isolator, dedicated space, etc. It is cool as hell and I had fun building it, but I am not likely to do it again. A quality cooler will work perfectly fine for the type and amount of trips I do every year.

I also don't like messing with OEM electronics. Even when done right (which many people & even shops fail to do), it is a lot of complication for little (IMO) gain.

The best setup is a portable one that you can put into the truck when needed, and remove at other times. Goal Zero systems, as overpriced as they are, have the right idea. I would build something similar, but likely using a pair of 6V golf-cart batteries (in series). Super light, tons of usable amp hours, little (or no) modifications to the truck, and easily removable.

Despite my hugely built truck with mods I truly enjoy and use...everything you say here is pretty spot on for most people, IMHO. I do love having a fridge 24/7 though ...and armor has literally saved me from mass destruction quite a few times now. But for most drivers, it’s not necessary.

 

[KLF]

Stop cluttering up this thread with common sense and logic!

 

[eatSleepWoof]

Stop cluttering up this thread with common sense and logic!

Sorry, sorry! Here, I'll make up for it:

Overland, brah! 50" lightbars! Six rotopax on every corner! Hi-lift + spare Hi-lift so you can lift hi while you hi lift high. Blue ridge overland gear boxers!

Better?

 

[Sandroad]

I really like the KISS of the OP. I would add 3 notes:

1) if you're buying 2 new batteries, for sure get deep cycle/hybrid batteries. Their internal construction will make a difference in longevity in this scenario.
2) If you go with a low voltage voltage protection mechanism, make sure it's auto-reset. When the stater is run, even a dual battery setup like this will momentarily pull the voltage down low enough to trip a low voltage detection device.
3) Don't bother with a voltage readout of a battery under load using a cheap device. That's such a coarse and variable way to check battery SOC and health it's not worth it. I'm in the "use a good battery monitor or nothing" camp.