Howdy all, haven't posted in forever so I figured I'd share my latest project. Got tired of my old F150 winter beater not wanting to start when temps were dipping down to the negative 15-20 range (northern Iowa winters suck btw), after trouble shooting a crappy 8 year old battery and nasty looking 20 year old factory 4 gauge cables I ended up going overkill and installed a new starter and starter solenoid, also got a new Diehard Platinum AGM battery, and made some new cables out of 2/0 welding wire. With that combination the truck fired up flawlessly even on a night when wind chills hit -45. That would have been enough for most people but I'm not most people... so I decided to go for ultimate overkill and install 2 batteries.

Being a member of a couple offroad forums I've read up plenty on people doing dual batteries in their tow rigs and buggies and whatnot, many members speak highly of the BWD/Borg Warner isolation relay (part# 3098) so thats what I chose to use for my install. The 3098 BWD isolation relay is originally used on older 6.2 and 6.5 diesel GM products to isolate the aux battery from the primary battery when the ignition is off. Basically its main purpose is to keep two dissimilar batteries from drawing off of each other, like what would happen if you wired two batteries directly together in parallel. The negative cable of the aux battery is ran directly to the negative of the primary battery. The positive of the aux battery is wired to the isolation relay, and then from the relay its wired to the positive of the main battery. The BWD isolation relay looks almost identical to a fender mounted Ford starter solenoid, the BWD has two large terminals which are wired between you positive battery cables. It also has two small terminals, one is ran to a battery ground, the other needs to be spliced into a circuit the has power only when the ignition key is in the run position. If wired correctly the BWD relay will give off a single somewhat loud "click" noise when the key is turned forward, this tells you the circuit is closed and your batteries are now connected in parallel and ready to crank you over.

Aside from the bwd relay I also snagged the drivers side battery tray, and coolant/wiper fluid bottles, from a 7.3 diesel. Once I removed my factory overflow bottle I was surprised to see the threaded holes for the second battery tray already existed in my fender, I literally just bolted it in. I did have to modify my air intake since there was now a overflow bottle sitting where my factory airbox used to live. All I did to the intake was cut the factory flex hose in half and moved the mass airflow sensor a foot close to the throttle body and stuck a cone filter to the mass airflow sensor. As a side affect the truck now has a rather tough growl noise under throttle, although no difference in power from this rigged up cold air intake according to the "seat of the pants" dyno.

Sorry I dont have any pictures to share, although I will post a video explaining it all. Basically my setup is as follows: Factory passenger side battery tray now houses a group 65 930CCA Diehard Platinum AGM battery. I used marine style terminals to connect homemade 2/0 gauge battery cables. One cable from the positive runs over to the fender mounted starter relay, the other goes down to the starter. For the negative/ground I ran a 2/0 gauge cable from the negative battery terminal down to the factory ground location on the side of the engine, there's also a small section of 2/0 gauge tying the engine ground down to the factory ground on the frame. I also grounded to starter directly to the negative battery cable with 2/0 gauge cable.

For the aux battery: I mounted the drivers side battery tray in what would be the factory position had the truck been born a diesel. Since I had a ton of smaller 2 gauge cable laying around from another project I used it for the aux battery (since buying 2/0 gauge gets a little pricey) My aux battery is a 775cca group 34 Duracell AGM that I had sitting around. The ground from the aux battery is run directly over to the ground terminal of the primary battery. I also added a second ground from the aux battery which grounds to a existing hole down on the drivers side frame rail near the steering box. The positive 2 gauge cable of the aux battery runs over to the BWD relay which I mounted next to the factory starter solenoid/relay over on the passenger side fender. Then from the BWD relay I ran a short piece of 2 gauge to the positive of the primary battery.

So to sum things up... new starter, starter solenoid, and now 1705 cold cranking amps flowing through 2/0 gauge cable. Even at 0 degrees outside that poor starter sounds like its gonna fly off into orbit now when I crank the key

Here's a video of the end result, nevermind my jury-rigged hose sling and the ratchet strap thats holding the coolant bottle in place, hope to have all the loose ends buttoned up soon, just need to grab a couple more brackets on my next trip to the pick-a-part yard.

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Cool! I like it

 

this is pretty darn cool! im going to make an attempt at this sometime soon! This sure beats buying a $3-400 battery from oddyssey with the same capabilities (more or less).

 

You don't need an isolation relay unless one of your batteries is completely shot.
Look at what wiring said diesels use -- In the 7.3 in this model truck, both batteries were put in parallel, with 2/0+ gauge wire between them(positive side -- negative side is two separate heavy leads directly to the block, and through it, to each other).
Makes things cheaper/simpler.

Remember, with batteries in parallel: Yes, the two will equalize if they are unequal. But unless you're discharging one of them(as in a RV setup or something) greatly, they already should be (mostly) equal when charging. And even if they are slightly off, the power from the more-charged battery is going into the lesser-charged battery -- it doesn't just disappear.

Just wire the two together, call it good. One less thing to fail on you.

 

Look into a Diehard Platnium battery through sears, they're basically a rebranded oddessey. The cases look exactly the same, they're rated the same, and they're both built by the same manufacturer. Only differece is the diehard is about $120 less and has a year longer on its warranty even.

 

Well yes you could just wire em straight together, which is the case on many diesels when you have 2 identical group 65 batteries in most cases. What I like about isolating the aux battery is that it truely makes it a backup... say for instance you have a large eletrical load placed on the vehicle while its off (someone leaves the headlights on over night or something along those lines) with the aux battery isolated from the primary battery its just gonna drain yhe main battery while leaving the backup battery fully juiced up to still be able to start the truck. Same deal if your going camping or running a winch or something, if you connect all your aftermarket electronics to the backup battery then you're free to run it down while still knowing its isolated from the main battery which will still fire the truck up when the times comes. Instead of the electrical load seeing the 2 batteries as one big battery and drawing off them both (like if they were wired directly together) the system now gives me the flexibility of having 2 seperate batteries, either of which will still spin the truck over on its own should the other be drawn to far down.

 

Did you have to do anything with the alternator? In other words, is your stock alternator enough to charge both batteries while you're toolin' down the road? Looks like a great mod. Probably overkill for most of us - but I think that's why I like it!!!

 

The load on the alternator is determined by how much electric power you are using. Adding batteries doesn't increase the load. Turning on more lights, running a starter or winch, those are the types of things that increase the alternator load.

The exception to that is if both batteries are pretty run down it will take twice as long to get them both recharged as it would if there was only one.

 

My stock alternator crapped out last year and I replaced it with a brand new 110 amp unit originally intended for a 7.3. At the same time I also replaced the factory 8 gauge charge wire and fuseable link with a 2 gauge wire and an inline maxi fuse.

 

This is cool! I'd suggest using a deep cycle marine type battery for the aux application. Regular automotive start batteries don't like deep discharges at all. They can deliver a lot of current but will be ruined quickly when used for powering inverters, winches, and the like and run down. Maybe 5 to 10 discharge cycles and they are done.

The deep cycle batteries are a lot bigger (and expensive) because they have thicker plates that are designed to better handle regular deep discharges. While an automotive start battery can recover from a complete discharge below 11 volts (leaving the lights on overnight for example) it will never quite have the lifespan it would have otherwise.

 

If you were using it in an application where you'd be continually running a battery down then a deep cycle would be the way to go. I prefer using dual purpose AGM batteries in all my vehicles. You pay more up front compaired to a conventional lead acid flooded battery, but AGMs last much longer and can recover from a total discharge much better then a standard battery. I've got a few old optimas and random no name agm's laying around that I use for running the winches on my trailers, just cant seem to kill the things, I'll run em down to the point that they couldnt even power a watch and they'll still charge back up just fine, a couple of em are 10+ years old.

 

Be careful running electric motors on low batteries. In electricity power (Watts) equals voltage times current (amps). As batteries wear down they lose voltage, so to make the same power a motor needs to draw more amps. More amps will generate more heat in the windings.

I once ran an on-board air compressor long enough without the engine running that the battery voltage dropped, the current went up and the air compressor motor melted it's windings. I had no trouble starting the truck engine because it had a dual battery set-up and the compressor had only drained the isolated auxiliary battery. But it wasn't cheap to get the compressor motor rebuilt.

I'm not saying you can't run a motor on a near-dead battery. If the load you're putting on the motor is low enough, or if it has a very good cooling fan, or if it has an internal thermal shut off you'll be fine. But as I led off with, be careful doing this..

 

Interesting - sounds like those AGMs are the way to go. With all the rebranding going on it's bad enough but different price points means sometimes different construction altogether.

For example a Die Hard Platinum is now made by East Penn / Deka and Pretty sure that's AGM. I have a Die Hard Gold, another East Penn battery but not sure if it's AGM or not.

 

thanks for the info, years ago I had a towtruck with electric winch, & used tripple batteries, 1 was for cranking, 2 were hooked to run the winch, as well as warning lights & a seperate flasher circuit with aux bulbs in each light housing, so I could leave flashers on & light, & run winch, and save gas not leaving engine running, for charging I had used a battery isolator kit. still got the wrecker parts & have considered fixing up another wrecker, currently use a car trailer to tow cars with. I will look into this.

 

Diehard gold would be the brands highest quality standard flooded lead acid battery, its not a AGM. Still a good battery though. I work a few hours a week at an autoparts store, so pretty much anytime someone turns in any brand of AGM battery for a core I'll swap it for one of my junk ones. Theres actually a trick to charging a completely dischanged AGM, years ago someone showed me... you hook a completely discharged AGM in parallel to a charged standard battery with jumper cables, and then you put a trinkle charger on the good battery. Unless the AGM has a dead cell or is physically damaged I havent found one I couldnt put back in to service. Most people just think they're toast when they throw their charger on it and it wont take a charge.