2009 Suburban 2500 (GMT900) - Aux Battery System Concerns

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

irishcreamer

TYF Newbie
Joined
Oct 8, 2020
Posts
19
Reaction score
11
Hi everyone. Trying to add an auxiliary battery system to my 2009 Suburban 2500 and hitting some snags. Very much appreciate any insights you can provide.

The general plan is simple:
- Add second battery for auxiliary items and to serve as backup to the starter battery
- Isolator / Combiner
- Aux battery will drive some dc devices (radio, etc.) and an inverter
- Eventually I may upgrade the alternator (if needed) and add solar

Where I'm getting hung up:
(1) How does the aux battery interact with the EPM battery management systems and logic?
- What special treatment is required?
- I read about a current sensor on the starter battery ground cable for similar vintage Silverado but didn't see one at first glace

(2) What battery sizes fit in the aux battery tray located driver behind headlights
- Would be great to fit a Group 24 but I think it is too long...what are you all using here?
- Dealer said Group 48 does that sound right? I've seen examples online of Group 34


Tried running the EPM question up the line at both the dealer and directly with Chevy with no success. Hoping for a better result here.

Thanks!
IC
 
OP
OP
I

irishcreamer

TYF Newbie
Joined
Oct 8, 2020
Posts
19
Reaction score
11
Seems this is a hidden or boring topic...

After a bit of research and wire tracing I am reasonably certain of the current wiring:
  • Primary Battery Grounds (2)
    1. Battery cable to engine block
    2. Light wire to passenger side lower bumper frame (??)
  • Primary Battery Hot Leads (2)
    1. Battery cable direct to below engine (??)
    2. Battery cable to junction w/ 175A fuse
  • Junction Box After Fuse
    1. Battery cable to alternator
    2. Battery cable to factory driver side fuse panel

Open questions:
  • Are there any special EPM considerations when adding an Aux battery?
    • I was unable to find any current sensors on the battery wiring and now believe the 2009 Sub 2500 is wired differently than the same vintage Sub 1500 or Silverado.
  • What is the purpose of the relatively light wire to what appears to be the frame? Doesn't seem fit to carry much load so perhaps just to ensure the frame is grounded?
  • What is the largest size Aux batter I can fit in the stock tray?
  • Who makes a good inverter? And where to mount it inside the cab?

For those curious or interested in discussion, I'm sharing my draft wiring diagram for the Aux battery.

Best,
IC
 

Attachments

  • sub_dual_bat_draft_20201010.pdf
    92.8 KB · Views: 17
Last edited:

Doubeleive

Wes
Supporting Member
Joined
Nov 7, 2017
Posts
23,741
Reaction score
34,721
Location
Stockton, Ca.
Seems this is a hidden or boring topic...

After a bit of research and wire tracing I am reasonably certain of the current wiring:
  • Primary Battery Grounds (2)
    1. Battery cable to engine block
    2. Light wire to passenger side lower bumper frame (??)
  • Primary Battery Hot Leads (2)
    1. Battery cable direct to below engine (??)
    2. Battery cable to junction w/ 175A fuse
  • Junction Box After Fuse
    1. Battery cable to alternator
    2. Battery cable to factory driver side fuse panel

Open questions:
  • Are there any special EPM considerations when adding an Aux battery?
    • I was unable to find any current sensors on the battery wiring and now believe the 2009 Sub 2500 is wired differently than the same vintage Sub 1500 or Silverado.
  • What is the purpose of the relatively light wire to what appears to be the frame? Doesn't seem fit to carry much load so perhaps just to ensure the frame is grounded?
  • What is the largest size Aux batter I can fit in the stock tray?
  • Who makes a good inverter? And where to mount it inside the cab?

For those curious or interested in discussion, I'm sharing my draft wiring diagram for the Aux battery.

Best,
IC
the positive battery cable that you are referring to going under the engine in fact goes to the starter.
the epm that you are referring to is called "RVC" regulated voltage control and I believe the 2500's do not utilize it so nothing to worry about there.
anything metal on the vehicle unless it is isolated by plastic will function as a ground
your best ground will be the frame, the engine is grounded with a cable on purpose because it is mostly isolated by rubber from the frame (engine mounts, transmission mounts, etc)
 

PG01

Supporting Member
Joined
Nov 6, 2016
Posts
14,766
Reaction score
17,893
Location
Up here to the right
As doubie said and there are many options for dual batts. Factory to aftermarket. There are full write ups and many sub categories on the subject here and diff truck forums
@Tozan @intheburbs myself and @Doubeleive have all done dual batteries

I found most of my info when I did it for my 13 from upfitters guides some guys here have a factory isolated system, a factory parallel system as there were a few ways all these trucks (ppv/ssv SUV’s and diesel and non diesel pickups, 1500’s 2500’s etc left the factory) there are kits you can buy with everything you need and parts lists all over.

There’s no correct way, just options as to what fits your needs.

You can put whatever size battery you want if you want to fabricate but a group size 48 fits stock tray. 34/78 fits fine also you just have to mess with side/too mount configs.

I’m trying to think of option codes for a factory dual battery setup and tp2 comes to mind as does au2 but I could be wrong.

https://www.gm-trucks.com/forums/topic/75814-dual-battery-gmt900/

https://www.gm-trucks.com/forums/topic/102220-how-to-gmt900-auxiliary-battery-installation/


just a few other threads but there are some here as well
 

intheburbs

Full Access Member
Joined
Aug 10, 2017
Posts
775
Reaction score
1,343
Location
SE MI
Looking at your diagram, you need some more fuses. All leads from your positive terminals need to be fused, unless you're a fan of melted wires and possible vehicle fires. My setup uses all factory parts from the TP2 SSV option. The mega fuse holder on the passenger side firewall is replaced/enlarged to hold a second mega fuse, 125a, for the aux battery.

I've had my setup for 6 years, no issues.

I added dual batteries to both of my GMT900 trucks. Heres the thread I used and posted on...

https://chevroletforum.com/forum/tahoe-suburban-diy-useful-threads-61/aux-battery-tp2-upgrade-65109/
 
OP
OP
I

irishcreamer

TYF Newbie
Joined
Oct 8, 2020
Posts
19
Reaction score
11
Thanks everyone for pointing me in the right directly. I feel good about the overall design concept and am no longer worried about the EPM/ RVC.

Will work with a local shop on the installation so it gets done right. Will report back.

Just wish the 2nd row seating had clearance for the inverter.

-IC
 

JS73

TYF Newbie
Joined
Aug 15, 2021
Posts
1
Reaction score
0
Thanks everyone for pointing me in the right directly. I feel good about the overall design concept and am no longer worried about the EPM/ RVC.

Will work with a local shop on the installation so it gets done right. Will report back.

Just wish the 2nd row seating had clearance for the inverter.

-IC
I have done all mods you mention, including fitting inverters under rear seats. I have learned many things the hard way, but got it all working over almost 20 years of hands-on education…plus three engineering degrees for what thats worth, if anything.

I have three (2001, 2002 and 2003) Sub and Tahoes I keep two of in almost show condition, not a scratch, but use like they were intended to be. $164k in one and $187k in other over life. Third is a beater. I had all three since new and keep track of $. All have custom built 5.3/6.0L engines putting out 456HP to 512HP to wheels on Dyno. Whole other two decade saga there to pull as much power out of the awesome LS motors. One truck has had four engines if that is a hint.

Dual Batteries: From a technical perspective it is always best to use the same exact battery of close age and use for all applications where you will draw down current in parallel from. Deep cycle hybrid starter batteries that are both made for high amp quick draws to starter, and for powering slower even draws for amps, inverters, lights, etc. are technically your best bet. An AMG battery is my top pick. I use the 78s Optima Yellow tops. They fit and bolt in both main and 2nd tray without rigging or fuss. I know some people hate Yellow Tops, and they are $$$$. But I have tried just about all batteries that meet the above specs and these are the best bet for my applications. The one truck has two captains chairs for 2nd row, I took out bench, it has two 4500 RW pure sine flat yet wide inverters under the seats, one under each, with a third yellow top in where the factory sub was, and quick attaches to add the five additional yellow tops behind the third row seat in battery boxes, this bank of five batteries can be removed when not needed. My power application needs are going to be much greater than many peoples, these are company trucks for a property management company and are lifted 2-6” with 33-35” tires for a reason. We dispatch them in storms or other events when properties have prolonged power outages. Point is I need the power.

I added an easy to use AMG battery capacity sensor system, another saga, that works with the trucks fleet management systems that includes remote start. So we can leave a truck at a site and it will power what we have wired as essentials in the houses or multi-unit buildings for days, they self-start to recharge battery bank.

Some tips:

Buy a good 200-250amp alternator. Don’t play with the dual alt BS kits. A 130amp “high output” alt will not cut it if you exceed a 2000w running watt, 3000 peak for example inverter. One high quality high amp alt.

I use the Yellow Top as primary batteries as well. This has to due with the charging cycle and built-in electronics in modern quality AMG or other Deep Cycle batteries. Not to nerd out, but each battery will be connected while charging, even with an isolator. It is not a major deal, but you will get more life out of at least your primary if all batteries are the same.

Why use the Yellow Top dual purpose bank for accessories and inverters? Because having the starter draw capability, which is built into batteries electronics to sense, means you can use your 2nd, 3rd, etc. battery to start your truck if needed. A back-up. Note: A deep cycle battery will start your truck, but it will reduce the life of the uni-purpose battery in many cases. Now there are some deep cycles that this does not apply to. I do not wish to get into religion re: batteries. I can only say what I use and why. Many years ago I helped design batteries when the new concept of adding a “brain” to them came out, this was when I was an engineer, a lot has changed. A lot has not changed. If someone knows more about current battery embedded electronic control systems please add.

Isolators: What a struggle. We use a mix of various brands and after years of trying various ones I am not going to recommend a certain one. They all suck unless you drop some serious money, and then the just suck a little less. I found the most critical things are it be rated at 250amps running amp, or rated at 50 amps over your alternators max amps to be safe. Some Isolators are rated at max running throughput, others a peak (spike) max. Most do not say which. So go big. Technically a 250amp alt is not going to produce near that unless there is a draw requiring it. Which could happen, but in reality the ratings on alts are at max draw not running amps.

Someone mentioned fuses to prevent burning up wires or your truck. This is very real and very critical. After years of using slot and bar style fuses we switched to waterproof 250amp breakers. I suggest you go overkill on the breakers or fuses. The breakers have manual trips and are therefore switches as well. All hot wire runs should have one. When in doubt fuse or breaker it. Having more safety is better than more risk. Just make sure you can get to them all, and remember or document where they are.

Wire to use: 1/0AWG pure copper flex (strand) and very high quality crimp on connectors; Do not skip the shrink sleeves on all connections! It may sound like a lot of work, but after doing a few it is easy. Buy large gauge wire cutters, strippers and an actual 1/0 crimping tool. YouTube for best practices making your wires.

Note: When putting in a 200-250amp alt, 2nd, 3rd etc. battery and an AC inverter you go from a 12volt DC at 100amps max system to a system that will kill you or others due to basically using the truck engine to produce both DC and AC current at a whole other leave. If you have kids who ride in the truck, those breakers that quickly shut the current and system off come in handy. I trip my breakers if anyone is riding in the rear. More on safety below.

I also have a lower wattage inverter system in the Tahoe I drive daily. It has house style plugs in a few places to power laptops, etc. I like the ones with built in USB charge ports.

Safety expanded: I do not plug stuff into the inverters directly. I make plug cords out of 12/2 Exterior Romex wire and sleeve it in auto grade flex tube, then run that feed to a GFI plug, usually in rear, then daisy chain the interior other outlets off of the load side of GFI. The tricky part is what acts as ground on the given inverter. I can help you figure that out if needed if you have a multi-meter aka Volt Meter. In many cases the ground of the inverter is what will enable the GFI to work (trip if hot comes into contact with ground. In the case of inverters with ground wire in common with plug outlet ground make sure to wire it with a solid copper 12ga (I pull a ground wire from 12/2 Romex and make two runs to ground from inverter ground, Not The Plug Ground) the ground on inverter to both your frame and body, it is critical. I have seen many people skip connecting ground or screwing it into isolated metal (which is not grounded). The simple a safest way is to buy an inverter that has GFI built in. Something like this one:

Cotek SP-2000-112 Pure Sine Wave Inverter with Dual GFCI 120VAC 12VDC 2000W​

I am NOT recommending this unit, I just want to provide an example of a flat unit that should fit under 2nd row seat AND has the GFCI feature.

Note: If you do not know what Pure Sine Wave is please google and YouTube it. You may need it, you may not.

Note: If you buy a cheap inverter you get what you pay for. Please keep in mind that if you buy an inverter without GCFI built in and plan to use a GCFI power strip to save a bit, you must ground the inverter properly or the GFI feature of power strip will not work.

In general finding the right inverter for you will take some research. A tip is to look at the output of the actual outlets to calculate the needed capacity for which one to get. The 2000w, 8000w, etc. means very little. There is no standard rating system for these things. The outlets and there capacity is key. Match that to your application. I seem to be on a wordy roll, so I will mention that when calculating the outlet capacity look to see if the outlets are a banked draw, or individual capacity. Meaning if you do need a 15amp circuit at 110V or 1650 watts, does one outlet support that? I can tell you that the high wattage units are certainly not banked, where all power is available via one outlet (as in a master bank of power any one outlet can draw on),. They are usually 10, 15 or 20 amp outlets individually. If you used all outlets at once to max capacity before tripping then you theoretically could hit the max rated wattage of the inverter. This would mean you need a bigger inverter. There are some that come with a large feed outlet, 30amps is our largest. We use RV 30amp hook-up cords for those. All our trucks with those have a 30amp RV hook up port mounted to the bumpers, we cut square slots and mounted them so they look clean and covers match bumper finish so they blend. Again, this is a dangerous amount of current, even the 15amp circuits could kill someone. You will find not many quality auto service places will mess with installing an AC current system, and not many res/commercial electricians will mess with putting AC current into a car. They do not cover that in training and if they are licensed they will not touch it from what we found. There are a few custom car audio shops that will put them in. But do they know what they are doing? When your project is done, buy a $5 GFI tester and check all outlets to make sure they trip in the event the hot grounds to prevent shocks. And remember to only run the system when in use. Buying the remote on/off switch is smart, if it does not include one. Just remember the inverters themselves have an ON button and little kids bored in the truck will find it. A cool button to try. This, trip the breaker to the unit so it can’t be turned on.

I went off on that subject. There is a lot more to it, if you have questions or see something I messed up reply. All the above is only my opinion and should not be used as an installation guide.

Good luck
 
OP
OP
I

irishcreamer

TYF Newbie
Joined
Oct 8, 2020
Posts
19
Reaction score
11
JS73 - Wow what a wealth of information. Thank you for sharing. Very cool concept with mobile on demand starting.

Work had me distracted lately and I see it's been some months since I engaged here. Actually had the system installed by a local car audio specialist before seeing this post. Generally very pleased with his work and he seemed quite confident and capable. If I did it again I would insist on tinned marine wiring and shrink over the crimps... boat style.

General overview:
- Replaced Main battery and added Aux battery in stock tray - pair of Interstate MTZ-48 H6 (AGM dual purpose, 70Ah)
- Connected the batteries in parallel when charging with Blue Sea Systems ML-ACR 7622 (500A ACR with manual control and remote switch) mounted to passenger side of engine bay between Main battery and wall
- ACR remote switch and Blue Sea 1733 voltmeters below dash on side of console (driver's right calf area)
- Ran power from Aux Battery through a breaker to KISAE SW1220 (2000W sinewave inverter with GFCI and remote switch)
- Inverter is installed behind second row passenger seat, mounted to frame of Cargo Glide CG1800HD (they have a submodel that mounts directly to the third row seat bracket)
- Ran power from Aux Battery through a breaker to a Blue Seas ST Blade Fuse Block in the rear side storage compartment behind the jackstand
- Added VIAIR 400H-A onboard air compressor in this rear compartment and routed the air hose through the plastic near the window (also added a relay and switch in the rear)
- Ran power from Aux Batter through a breaker to a Blue Seas ST Blade Fuse Block in engine bay. This will allow for expansion.

Offhand I'm not sure of the breaker and wire sizing - I know we discussed oversizing the wires... have notes somewhere to update my project summary.

Next steps for the truck:
- High Output Alternator (if you have any recommendations I am all ears)
- Roof Rack - seems all the cool custom stuff is only for Toyota :(
- Roof Top Tent
- Removable solar charger wired into the Aux battery


Thanks,
IC
 
Last edited:

Imlow78

Full Access Member
Joined
Sep 29, 2021
Posts
122
Reaction score
179
Does GM not offer a wiring harness for the TP2 or 8BO options that a plug and play?

Or is it DYI only?

Shannon
 

mikeyss

Full Access Member
Joined
Nov 11, 2011
Posts
1,626
Reaction score
3,042
Location
Longmont, Colorado.
Does GM not offer a wiring harness for the TP2 or 8BO options that a plug and play?

Or is it DYI only?

Shannon
Gm offers both, I believe rockauto sells them. I got my dual battery factory setup parts from them, using the factory wiring setup where the battery positives both go to the starter, and the driver's side battery factory negative wire that goes to the alt bracket
 

Forum statistics

Threads
129,270
Posts
1,813,079
Members
92,378
Latest member
Luggz
Top