Adding Auxiliary Battery?
Thread Starter
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Joined: May 2020
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Adding Auxiliary Battery?
Hey all,
I've been lurking on this site off & on since I got my truck in Dec. 2018 - it's been a good to read about others' issues and learn by proxy.
I've finally got something of my own to ask about. I tried searching old posts and couldn't find anything solid to help me with this, but if I missed one please just point the way!
I use my truck for rental property maintenance/handyman work, etc., and I'd like to add an inverter in the truck bed toolbox so I can have some drill batteries charging/plug in corded tools from time to time, etc. I saw mention of an optional second battery in the owner's manual, and I've come across some posts online debating the use of relays vs. isolators, etc. for this purpose. Obviously I don't want to have to worry about draining my starter battery, and while I'm comfortable working on this stuff, I'm not nearly experience enough with automotive modifications to go about designing a system for myself.
Does anyone have any guidance on a good walk-through/tutorial for this with a parts list? Is there a second battery bracket that Ford made that I might be able to order/source at a junk yard? Thoughts on relays vs. isolators (I've seen lots of conflict on this point)?
I've also seen that I'll likely need to upgrade my alternator for this project - any input/thoughts on that?
Any advice on this would be much appreciated!
WW
Editing cause my signature didn't work for some reason:
1984 F150 XLT - 302ci w/ AOD
Single Cab/Short Bed (117 W/B) - 3.55 GR
Yokohama Geolandar A/T-S (P235/75R15)
175k miles - Dual Tanks/Cruise/AC
Added 4-pin trailer connection for step bumper hitch
I've been lurking on this site off & on since I got my truck in Dec. 2018 - it's been a good to read about others' issues and learn by proxy.
I've finally got something of my own to ask about. I tried searching old posts and couldn't find anything solid to help me with this, but if I missed one please just point the way!
I use my truck for rental property maintenance/handyman work, etc., and I'd like to add an inverter in the truck bed toolbox so I can have some drill batteries charging/plug in corded tools from time to time, etc. I saw mention of an optional second battery in the owner's manual, and I've come across some posts online debating the use of relays vs. isolators, etc. for this purpose. Obviously I don't want to have to worry about draining my starter battery, and while I'm comfortable working on this stuff, I'm not nearly experience enough with automotive modifications to go about designing a system for myself.
Does anyone have any guidance on a good walk-through/tutorial for this with a parts list? Is there a second battery bracket that Ford made that I might be able to order/source at a junk yard? Thoughts on relays vs. isolators (I've seen lots of conflict on this point)?
I've also seen that I'll likely need to upgrade my alternator for this project - any input/thoughts on that?
Any advice on this would be much appreciated!
WW
Editing cause my signature didn't work for some reason:
1984 F150 XLT - 302ci w/ AOD
Single Cab/Short Bed (117 W/B) - 3.55 GR
Yokohama Geolandar A/T-S (P235/75R15)
175k miles - Dual Tanks/Cruise/AC
Added 4-pin trailer connection for step bumper hitch
Last edited by wesley.wittich; May 27, 2020 at 03:39 PM. Reason: Signature didn't work
Member
Joined: Jan 2018
Posts: 11,256
Likes: 1,769
From: Memphis, TN, Earth, Milky Way
Study this diagram, its caption, & the links in it:
(phone app link)
Putting a substantial inverter in a bed toolbox is VERY risky because 1) it will require substantial power wires connected directly to the battery, like a winch; and 2) the wires will have to make several bends past sharp edges transitioning across parts that move differently. If the hot wire ever shorts to ground, it will likely set itself & anything nearby on fire, and detonate the battery. There are ways to mitigate the risk, but they're fairly intricate and have their own limitations. I recommend you consult a pro, like someone who works on ambulances or a stereo/alarm installer. Typical mechanics (including those who install winches) are not usually familiar enough with these special wiring considerations. Some of them are explained in this caption:
(phone app link)
The only alternator you should consider is the 130A 3G, which is a popular swap on early Broncos (which also have V-belts like yours). You can find many discussions about that swap at https://classicbroncos.com/forums/forumdisplay.php?f=42
(phone app link)
Putting a substantial inverter in a bed toolbox is VERY risky because 1) it will require substantial power wires connected directly to the battery, like a winch; and 2) the wires will have to make several bends past sharp edges transitioning across parts that move differently. If the hot wire ever shorts to ground, it will likely set itself & anything nearby on fire, and detonate the battery. There are ways to mitigate the risk, but they're fairly intricate and have their own limitations. I recommend you consult a pro, like someone who works on ambulances or a stereo/alarm installer. Typical mechanics (including those who install winches) are not usually familiar enough with these special wiring considerations. Some of them are explained in this caption:
(phone app link)
The only alternator you should consider is the 130A 3G, which is a popular swap on early Broncos (which also have V-belts like yours). You can find many discussions about that swap at https://classicbroncos.com/forums/forumdisplay.php?f=42
Thread Starter
Junior Member
Joined: May 2020
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Thank you for the resources, Steve! Looks like I have a lot of reading to do 
Do you think there would be a better way to route power to the bed of the truck? Such as mounting an inverter closer to the battery (even in the engine bay?) and then routing normal AC power to the truck bed, which would allow it to be much lower gauge? I could also potentially use some sort of in-line fuse/breaker at that point to cut off if there was a cut/short in my toolbox/bed wiring. My chargers for drill batteries, etc. won't draw a ton, and my need for running other tools will be rather intermittent so if there is a better/safer layout I'm certainly open to that...
Do you think there would be a better way to route power to the bed of the truck? Such as mounting an inverter closer to the battery (even in the engine bay?) and then routing normal AC power to the truck bed, which would allow it to be much lower gauge? I could also potentially use some sort of in-line fuse/breaker at that point to cut off if there was a cut/short in my toolbox/bed wiring. My chargers for drill batteries, etc. won't draw a ton, and my need for running other tools will be rather intermittent so if there is a better/safer layout I'm certainly open to that...
Member
Joined: Jan 2018
Posts: 11,256
Likes: 1,769
From: Memphis, TN, Earth, Milky Way
It would be very laborious for me to explain all the possibilities & options in text. You should look for a local installer who understands them and can discuss it with you F2F.
Decent power inverters have built-in protection for their outputs. And like audio amplifiers, they're not generally designed for exposure to weather or underhood conditions - they need to be dry & cool, so the cab is the best place for them. This is where I mounted one in my F150, but I haven't really used it for anything yet:
(phone app link)
I brought its wires through the factory grommet on the HVAC blower box under the Right hood hinge, into the kick panel, under the threshold, and up the B-pillar to that location.
Decent power inverters have built-in protection for their outputs. And like audio amplifiers, they're not generally designed for exposure to weather or underhood conditions - they need to be dry & cool, so the cab is the best place for them. This is where I mounted one in my F150, but I haven't really used it for anything yet:
(phone app link)
I brought its wires through the factory grommet on the HVAC blower box under the Right hood hinge, into the kick panel, under the threshold, and up the B-pillar to that location.
