1600 Amps On Tap -- Painless Performance Dual Battery System Installat

jthelman · April 3, 2011

So I figured I'd post my installation of the Painless Performance 40120 dual battery system.

This is installed on a 2008 GMC Sierra 1500 extended cab. My truck had a second empty battery tray and a high amp alternator from the factory.

The painless performance kit is an alternative to the GM dual battery system. It automatically detects when the main battery is under load and kicks in the secondary battery when needed. It also manages to charge both batterys. All of this happens without any user intervention.

Total cost was $180 for the 40120. I bought at Summit, but Jegs and others carry it.

$130 second battery (Autozone Duralast 34D 800 CCA)

$15 miscellaneous stuff like marine terminals, battery hold down, extra lugs, etc.

The filthy engine bay was free....

About $325 total.

The system has a very straightforward install.

1) I mounted marine terminals on my second battery, then dropped it in the car. I bought a hold down 'foot' and bolt from Autozone to keep the battery in place.

2) Mount the 40120 unit. The unit comes with through bolts and nuts, but there really isn't anywhere I could bolt it down that had access to both sides of metal for the nut system. Instead I used pop-rivets and mounted the unit on the firewall (same deal as Craig, clc3251).

3) Ground the new battery, and the unit. There's a convenient bolt right next to where I mounted the 40120, it mounts with the engine grounding strap and works great.

4) Run two positive leads from the 40120 to each battery. On the GMC main battery, there isn't much (any!) room on the battery terminal. If you go up onto the firewall, you can use the bolt for the fusible link, this makes it a lot easier!! See Pics.

My installation used marine battery terminals so that it's easy to disconnect the 2nd battery when working on the car; just spin off wing nuts and remove the leads.

Optional: You can run 2 wires for an indicator light painless provides in the kit. The indicator light will tell you what the system is doing under the hood (charging both, tapping the 2nd battery for help, etc...). If you look at the pics, you can see that I mounted my indicator light below the DIC buttons. The dash panel on the left side of the dash pops off pretty easily, and you can remove the DIC buttons to drill a hole. Very easy install. Thanks to "SuperPerv23" for suggesting that I run the wires through the grommet the hood release comes through the firewall -- that works great!

I made one modification to the painless system; the indicator light is *WAY* too bright, especially at night. Under normal operation the light pulses on and off, and it was extremely distracting to have a super bright pulsing blue light on the dash. Your natural instinct to that a flashing light means something is wrong. I wish they didn't design the system this way, but that's the way it goes....

My solution to the indicator problem was to install a 150 Ohm resistor in the positive indicator lead from 40120 box. If you look at my pics, you can see the resistor installed under the heat shrink tubing. The resistor cut the brightness by 50%ish. On a sunny day I might have to cup my hand over the light to read it, but it is much better than before. At night the light is visibly pulsing, but not screaming at me! The last 2 pics show the light on and off on a fairly sunny day.

If you are going to do a dual battery install, this kit seems like the way to go. Easy install, and no user invervention needed to make everything work.

Now I can install that inverter.

Feel free to reply or PM me and I can try to answer any questions.

Link to pics: https://picasaweb.google.com/john.thelman/P...gCLTptb6tp7GXaQ#

John

Sir Dan · April 4, 2011

Nice install! I've been toying with the idea of a dual set up too, but the stock system I've seen a few posts on seems way too complicated. Painless Performance really looks "painless"!

907steve · August 1, 2012

Hey thanks for the write up i have a question though... My blue light never turns on and i cant tell if this thing is even working ? i purchased a brand new battery and its reading 12v same as my stock. it says it could be in standby mode if the light doesnt turn on. I dont have anything light a winch to test it. have any ideas on how i can see if this thing works ?

Gurrzt · August 1, 2012

Very nice & VERY CLEAN.

Hoe-n-it · August 8, 2012

Hey thanks for the write up i have a question though... My blue light never turns on and i cant tell if this thing is even working ? i purchased a brand new battery and its reading 12v same as my stock. it says it could be in standby mode if the light doesnt turn on. I dont have anything light a winch to test it. have any ideas on how i can see if this thing works ?

I don't have this installed yet but I'm seriously considering it and have been doing a lot of research. From a post on another forum, the way to test it is to run down your main battery with lights etc and then start the vehicle. Except for charging the auxillary battery after the main battery is fully charged, the only time it will combine the 2 batteries is when it detects a large amp draw that the main battery can't satisfy.

I don't use my Tahoe as my daily driver and it sits sometimes for a week or two. I was loading up for a vacation trip with doors, tailgate open several times and went to start the vehicle and nothing. Jumped it but was worried the whole time that it may not start. I think I will get the Painless setup for piece of mind.

Sir Dan · August 8, 2012

I ended up getting the painless system and it is easy to install. Never have to worry about a dead battery again.

cl12253 · August 23, 2012

This is JUST what I've been looking for... signed up for the forum specifically to say "Thanks" for the excellent write-up.

Planning on working an inverter into the equation, too -- so I'm looking at a DieHard Platinum Marine (AGM, deep discharge, on sale as of 8/22/12), add it as the aux, and run the inverter off it.. The Painless should protect the primary from any draw (right?) so my only concern would be monitoring voltage on the aux to make sure I don't run it down too low and damage it. Or am I missing something here?

Any input here would definitely be welcome, and thanks again for a great post!