Adding a Dual Battery

higsy · November 25, 2018

Can I test this from the top side where the fuses are or do I have to remove it to access the x50 connectors underneath.

RACERX7775 · November 25, 2018

Im telling ya, look to see the fuse box diagram. It will show what fuses are open, and what are spares. Then yes, use a test light to see if they are ignition fed or constant. Then, you could lift off the fuse block to get to the bottom.

1SLOW1500 · November 25, 2018

Wondering why you need a 12v(constant) and a switched 12v. For one the 12v is on both main posts or batt1 and batt2. And it should be ground and switched. As it is nothing more than a high amp relay. Also I would make sure you have a ignition wire or rap. Hate to have that cycle every time you turn the key.

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higsy · November 25, 2018

I'm installing as per oem installation. Tp2....this is a quote as to What is needed for wiring the relay and isolator.

With those items installed you have completed the install of the new hardware. Now it's time to tackle the wiring aspect. There are only 3 wires we need for this. Switched 12V (only hot when key is in ACC), constant 12V (always hot), and ground. Orange wire is used for switched 12V, red/wh is constant 12V, and black is ground. The two 12V wires will come from the fuse block and the ground will come from the passenger side head. The orange wire is technically the "ignition 3" circuit and is controlled by the BCM..

1SLOW1500 · November 25, 2018

I'm installing as per oem installation. Tp2....this is a quote as to What is needed for wiring the relay and isolator.

With those items installed you have completed the install of the new hardware. Now it's time to tackle the wiring aspect. There are only 3 wires we need for this. Switched 12V (only hot when key is in ACC), constant 12V (always hot), and ground. Orange wire is used for switched 12V, red/wh is constant 12V, and black is ground. The two 12V wires will come from the fuse block and the ground will come from the passenger side head. The orange wire is technically the "ignition 3" circuit and is controlled by the BCM..

Oh I see what they did there. Ok.
Again it is just like a big single battery as the batt2 does nothing till key is on then it connects to the other battery. Unless you wire accessories to the batt2 but what would that be that isn't controlled buy the key. I have seen trailer power.

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aaron85252 · August 17, 2019

On 6/28/2017 at 12:17 PM, Spurshot said:

I spent about $500 on parts, installing a second battery in my 2008 truck. The cost is dependent on whether you go with automatic charging management, manual charging management, quality of the components, method of battery isolation/connecting.

Do you have a BOM for the 2008?

Vuk · November 13, 2019

I am just finishing up my factory-style setup on my 2016 Sierra 1500.

The harness part # for this age is 23273450. It replaces the original wire that runs from the primary battery to the underhood fuse box (it contains this within the harness). It comes with the relay that controls the battery isolator ("secondary auxiliary relay"). It also includes the auxiliary battery positive terminal with a fuse holder adjacent to the terminal (populated with a 125A fuse), however, it does not come with the cover for this single-fuse box (part # for the cover is 22945779). If you would like to directly draw high gauge cables to accessories (e.g., inverter), you can get the 3-fuse holder from older models (19116352 and cover 15881616) so you get a 100% factory install with provision for accessories. This 3-fuse holder can replace the single fuse holder that comes with the aforementioned harness (just take the battery terminal off of the single fuse holder and set it on the 3-fuse block). In that case, the fuse block sits on the battery just like the single-fuse box would. The distribution block on the primary battery already has a blank 125A spot for the auxiliary battery harness (as seen in photos above), so no modifications are needed there - just some nuts (should be 21021808).

Auxiliary battery negative terminal with the wire should be 84354708 (I am still waiting for this last part to complete my setup).

The secondary auxiliary relay part # is 12135194. You will have to use either self-tapping screws or rivet nuts to mount it to the firewall.

Battery tray part # is 22989633, retainer is 14005061, and the retainer bolt is 11519527, as mentioned here earlier.

Next, you need the "X158 Auxiliary Battery Harness to Engine Harness" that supplies ground, (+), and the signal for the relay to the aforementioned auxiliary battery harness (if you don't want to make the connector yourself). Service connector part # is 19367564. If you want to go full-factory, you can get violet/brown and red/white wires online.

The black (ground) from the harness, I connected to the ground post on the firewall where the relay is mounted. The violet/brown connects to pin 42 of "X115 Engine Harness to Body Harness" connector near the underhood fuse box and the auxiliary battery. The "body" side of the connector is very accessible and there is already a violet/brown wire that you can tap into (that is the "Run Ignition 3 Voltage" signal). The red/white needs to go to pin G6 of connector X2 of the underhood fuse box - there was no pin in there so I used the terminated lead 19301767. I already had the F52UA fuse installed - that one will supply power for the auxiliary relay, so just adding the terminated lead was enough.

Everything works but I am surprised that the relay disconnects the batteries during cranking. Can someone confirm how the system operates? I was expecting the auxiliary battery to "help" during the cranking. I can clearly hear the relay engage when the key is in ON, but disengages during cranking, and engages again when the cranking is over.

Thank you!

gmcdawg · November 16, 2019

Based on pics from the first few pages of this thread, the only difference in the trays is the hole for the hold down with welded nut on the underside? Correct? Why buy another tray, I can modify my original tray with a nut easy enough. Am I missing something? Place the rubber hold down in the original tray, mark the hole, drill it out and weld a nut on the bottom side.

2003 SSEi · November 17, 2019

On 11/13/2019 at 8:40 AM, Vuk said:

I am just finishing up my factory-style setup on my 2016 Sierra 1500.

Thanks for the great post and part numbers. Do you have any pics of the install or the finished product.

1SLOW1500 · November 17, 2019

Ok call me cheap but for $7.00 you can buy a bolt and the plastic puck for the hold down then remove factory tray and there is a metal tap you just increase the angle on a very small amount. Reinstall tray and your done.
Tap is in photo 2

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1SLOW1500 · November 17, 2019

Based on pics from the first few pages of this thread, the only difference in the trays is the hole for the hold down with welded nut on the underside? Correct? Why buy another tray, I can modify my original tray with a nut easy enough. Am I missing something? Place the rubber hold down in the original tray, mark the hole, drill it out and weld a nut on the bottom side.

Hole is already there on mine and I just used a hardware store nut.

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1SLOW1500 · November 17, 2019

I am just finishing up my factory-style setup on my 2016 Sierra 1500.

The harness part # for this age is 23273450. It replaces the original wire that runs from the primary battery to the underhood fuse box (it contains this within the harness). It comes with the relay that controls the battery isolator ("secondary auxiliary relay"). It also includes the auxiliary battery positive terminal with a fuse holder adjacent to the terminal (populated with a 125A fuse), however, it does not come with the cover for this single-fuse box (part # for the cover is 22945779). If you would like to directly draw high gauge cables to accessories (e.g., inverter), you can get the 3-fuse holder from older models (19116352 and cover 15881616) so you get a 100% factory install with provision for accessories. This 3-fuse holder can replace the single fuse holder that comes with the aforementioned harness (just take the battery terminal off of the single fuse holder and set it on the 3-fuse block). In that case, the fuse block sits on the battery just like the single-fuse box would. The distribution block on the primary battery already has a blank 125A spot for the auxiliary battery harness (as seen in photos above), so no modifications are needed there - just some nuts (should be 21021808).

Auxiliary battery negative terminal with the wire should be 84354708 (I am still waiting for this last part to complete my setup).

The secondary auxiliary relay part # is 12135194. You will have to use either self-tapping screws or rivet nuts to mount it to the firewall.

Battery tray part # is 22989633, retainer is 14005061, and the retainer bolt is 11519527, as mentioned here earlier.

Next, you need the "X158 Auxiliary Battery Harness to Engine Harness" that supplies ground, (+), and the signal for the relay to the aforementioned auxiliary battery harness (if you don't want to make the connector yourself). Service connector part # is 19367564. If you want to go full-factory, you can get violet/brown and red/white wires online.

The black (ground) from the harness, I connected to the ground post on the firewall where the relay is mounted. The violet/brown connects to pin 42 of "X115 Engine Harness to Body Harness" connector near the underhood fuse box and the auxiliary battery. The "body" side of the connector is very accessible and there is already a violet/brown wire that you can tap into (that is the "Run Ignition 3 Voltage" signal). The red/white needs to go to pin G6 of connector X2 of the underhood fuse box - there was no pin in there so I used the terminated lead 19301767. I already had the F52UA fuse installed - that one will supply power for the auxiliary relay, so just adding the terminated lead was enough.

Everything works but I am surprised that the relay disconnects the batteries during cranking. Can someone confirm how the system operates? I was expecting the auxiliary battery to "help" during the cranking. I can clearly hear the relay engage when the key is in ON, but disengages during cranking, and engages again when the cranking is over.
Thank you!

First I have to state I am impressed. I was far to lazy to do the part search. I have a aftermarket relay and isolator and it connects only with key. Or when stock dies I can over ride the power to the isolator with a switch, that is powered by the 2nd battery. Start truck and switch back. This also means both charge as I drive.
I got around all day like this when stock was dead.

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Vuk · November 17, 2019

On 11/15/2019 at 11:13 PM, gmcdawg said:

Based on pics from the first few pages of this thread, the only difference in the trays is the hole for the hold down with welded nut on the underside? Correct? Why buy another tray, I can modify my original tray with a nut easy enough. Am I missing something? Place the rubber hold down in the original tray, mark the hole, drill it out and weld a nut on the bottom side.

The trays differ in two things. One is the hole for the retainer bolt - you can easily put a rivet nut there and you would be done. The second difference is the lip on the opposite side of the battery that holds the rear in (you lower the battery into the tray, you slide it towards the driver seat, the bottom edge of the battery locks into the lip on the rear, and then you put the retainer over the front edge). If I were to do this again, I would modify the old tray (now I found another project to use the old tray).

Vuk · November 17, 2019

9 hours ago, 1SLOW1500 said:

First I have to state I am impressed. I was far to lazy to do the part search. I have a aftermarket relay and isolator and it connects only with key. Or when stock dies I can over ride the power to the isolator with a switch, that is powered by the 2nd battery. Start truck and switch back. This also means both charge as I drive.
I got around all day like this when stock was dead.

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This factory setup will charge them both when the motor is running, I am just confused with the batteries begin disconnected during cranking. This may be a feature on these model years because the BCM can shut down stuff if the voltage gets too low to disturb cranking? But what would be the purpose for the factory aux battery then, if this is the case? I will have my own accessories, that is OK for me, but what would the factory-intended purpose be? Was the BCM software updated with this feature starting from 2016 when the aux battery package was not offered any more? Is this maybe the reason why the tray is replaced with the dummy version (that is, the BCM takes care of over-discharge so the aux battery is not as necessary any more)? This is just me thinking why it would disconnect the aux battery during cranking.

Edited November 17, 2019 by Vuk