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Adding A Second Battery Tray To a Ram  

Installing the tray that comes standard on the diesel under the hood of a Gasoline powered Ram
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Part Numbers for Diesel Battery Tray V10 Washer Bottle Battery Isolator options

Subject:     Battery tray
From:          Jeff Trithart <>

> Does anybody know what the part #'s are for the second battery tray that comes
> standard on the Cummins?

Battery tray   PN 55275126
Battery hold down  PN 55235142  need 2 pcs
Battery strap  PN 55275220  Need 1
Hold down nut  PN 6101308  Need 2 pcs

What is not listed is the 2 allen head bolts for the fender to tray mount and the 2 nut and bolts for the tray to inner fender mount, get these at your local hardware store, way cheaper.

The battery tray numbers above will set you back $69 canadian, US of A will be much cheaper!!

Jeff Trithart

Subject:     Dual battery installation

In a message dated 98-07-23 11:38:14 EDT, you write:

< On the V10 the washer bottle intrudes into where the second battery tray
< should go. Works fine for the V8 (and I guess V6).

I bought the V8 water bottle and modified my shroud to accommodate the bottle..
Works great.


Subject:    Dual batteries in 97 2500HD V10

I did this to my 97 V10 4x4 over a year ago.  See below for answers to your

> Question: Where does the diesel's coolant overflow bottle mount?

I mount on the passanger side of the fan shroud.

> Question: Where does the vacuum pump filter(?) thingie re-mount (I guess
>  the diesel doesn't have one of these)?

My doesn't have anything else on the passenger side.  Everything else is below the mounting area for the bottle.
> Question: How do I keep the transmission fluid cooler line from rubbing the
>  front of the new battery tray?
I pushed the to the side.  The hose did contact slightly, but the battery tray and the hose are fixed to near the same point.  I installed a trans temp sensor in this line, which moved it from contacting the tray.  Mine was touching the tray for over 1 year with no visible damage to the hose.

I also did not install an isolator.  My battaries are connect straight.


Subject:     Dual batteries in 97 2500HD V10
From:        Malcolm Blackhall <>

> More: I removed the old overflow bottle and the vacuum pump filter (I guess
> that is what it is).

I don't think its a vacuum pump.  Normally aspirated engines don't need vacuum pumps.  The engine produces all the vacuum you need.  Without a better description, I would guess that it is the air pump filter for the emissions control system.

> Question: Where does the diesel's coolant overflow bottle mount?

On the 99s it mounts on the side of the fan shroud with all engines except the V10.  So, it is a different design than on the V10.  I would guess that it is the same on 97s.

> Question: Where does the vacuum pump filter(?) thingie re-mount (I guess
> the diesel doesn't have one of these)?

You are right, the diesel doesn't have an air pump filter because it doesn't have all that emission control add-on crap.  You will have find somewhere to mount it.  I would try somewhere over the horns in front of the wheel well. You may have to fabricate a bracket to mount it and new hoses to reach the pump.

> Question: How do I keep the transmission fluid cooler line from rubbing the
> front of the new battery tray?

Haven't seen the modification you are attempting, but in general ... bend, clamp or reroute.  If there is a little play and somewhere to mount tubing clamps so that they will hold the line far enough away from the battery tray that they will not rub, I would recommend this approach.  Otherwise, you may have to fabricate new lines.

How does it feel to be an automotive engineer?

Subject:    How To (long) - 2nd battery tray in '98 v-10
From:       Harold Dahlstrom

I did just complete adding a 2nd battery tray in my 98 v-10. Unfortunately, Dodge didn't make it easy - v-10 owners just can't purchase the 2nd battery tray that the Cummins uses without coming up with some other coolant overflow tank. I wanted to keep mine, so I moved other stuff around and made my own.

What I did for my v-10 was to relocate the air pump filter down and to the rear - between the upper shock mount and the coolant overflow tank. I used one existing hole, and I was able to use 2 of the 3 studs on it's mount to secure it and it seems solid. I swapped the hose end-to-end and it routes cleanly. Then, I took the vacuum solenoid "thing" on the inside fender and moved it down near the horns, again using an existing hole. I did have to extend the rubber lines running to it, but the wiring was no problem.

Then, I used aluminum stock (typ 2" wide by 3/16" thick), both flat and angle to fab a platform. I went from the front structure on the passenger side of the radiator where there are 3 bolts - I used these to support the front of the structure. Then, I ran it to the back under where the coolant overflow tank mounts.

I bent another flat to run from the stock threaded insert on the inner fender down to the first link, and another from this, paralell to the first, back to the coolant overflow area.

All of this tied together created a platform I could rest most of my weight on! Then, I ran a piece of thinner flat across it with the ends bent up and drilled for the j-bolts and topped it off with a small battery tray from AutoZone - cut out for the last flat for the j-bolts.

Also, I wouldn't advise using aluminum with a "standard" battery that contains liquid - I'm using an (Interstate) Optima, so chances for corrosion are minimized. Also, the small footprint of the Optima makes this whole project easier.

Let me know if you have questions!


Is an isolator needed when paralleling batteries?

Connecting 12 volt lead acid batteries in parallel can be done, but you must be careful to minimize the danger of fire or battery explosion. Yes, manufacturers of diesel pickups connect batteries in parallel to provide the high starting currents required by diesels in cold weather, but the manufacturers take the lowest cost solution to the problem, and figure that the batteries will outlive the warranty period.

Batteries can be connected in parallel only if they are of identical age, capacity, and manufacturing lot, and only if they will always remain connected in parallel. If the batteries are ever cycled indepedantly, they should be replaced with another matched pair.

If a mismatched pair of batteries is connected in parallel and then allowed to sit, they will pass current back and forth in an effort to ballance charge. If one battery is weaker than the other, it will attempt to drain the stronger battery. Eventually, one battery will short and the other will then dump all remaing charge into the shorted cell - resulting in two dead batteries or worse, a fire or battery explosion.

To prevent charge swapping/discharging/fires/etc, some kind of isolator is recommended for batteries in parallel. There are two types of isolators:


A quality, sealed, heavy duty contactor is reliable and simple to install. A contactor connects an auxiliary battery to the charging system when the engine is running, and disconnects the battery when the engine stops. This allows one battery to start the vehicle and run the automotive systems, and the auxiliary battery to power winches, stereo systems, lights, transmitting equipment, campers, etc. The contactor also allows the auxiliary battery to boost the primary battery if the battery is dead and will not start the vehicle. Be aware that most auxiliary contactors can not handle starting currents, and all starter relays and solenoids will burn up if used continuously as contactors.


Isolators use high current diodes to split the charging current between two or more batteries. Vehicles with high capacity alternators must use very large diodes to prevent damaging the diodes when a discharged battery is recharged. The diodes introduce a voltage drop into the charging circuit of each battery that must be overcome by the alternator, which is not a big problem for most modern alternators. With a diode isolator, the voltage regulator must be carefully wired to prevent overcharging or undercharging the batteries. An isolator will not allow batteries to boost each other, but a jumper cable is better for that anyway. Isolators are much more expensive than contactors. Hellroaring Technologies has gained a popular following among the 4X4 crowd for their rugged isolator which has a very low voltage drop.

Archived RTML, DiRT, TD, and Cummins list postings

Subject:     Dual battery installation

I've had my USAmps battery for over 7 months now and 0 problems.  I used 2 gauge wire for the hook up, and no isolator.  No problems even when blasting my Kicker ZR360 amp, which can draw up to 80 amps.

Subject:     Dual battery installation
From:        Kevin Warren <>

Here are two quotes from rtml

I hope you knocked on wood there guy.  When wiring normal batteries in parallel with each other it is crucial that the batteries not only be the same size and amperage, but same everything (i.e. same manufacturer, built close to the same time, etc.).  Only batteries that are exactly the same have a good chance of working well together over a long period of time.  Eventually what will happen with your batteries is one will discharge the other, mainly because the two batteries have different internal resistances.  The USAmps batteries have the lowest of internal resistances (5 milliohms) and this is the reason why they can be used with any other 12 volt battery in parallel.

Re: [RAM] Cummins Dual Batteries
...there is no isolator. there is no "dedication" of duties for one battery vs. the other.  Each battery grounds to its side of the engine block.  the positive terminal of the passenger side battery goes via heavy gauge cable to the clamp bolt on the driver's side battery.  the auxiliary body ground goes to the driver's side battery.  the positive feeds go from the positive clamp on the driver's side.

Kevin Warren-Ben Lomond-CA

Subject:     RV battery isolator
From:        KI4CY <my email address>

> Does anyone out there have recommendations on how to hook up an isolated
> RV battery.
> Also I want to wire in an RV battery for the camper that will be charged
> while driving, yet be isolated so the camper doesn't drain the vehicle
> battery while sitting.

A solid state isolator is basically a pair (or more for multiple aux batteries) of high current diodes with a common anode. One cathode goes to the main battery, and other cathodes go the the aux batteries. The expensive (over $100) isolators use shottky barrier diodes and drop about 0.3V under full load. Cheaper isolators use silicon diodes which can drop over a volt under load.

For proper voltage regulation with an isolator, the voltage regulator sense lead MUST be connected at the main battery terminal of the isolator, not to the charge lead from the alternator (which means that alternators with an internal regulator do not work properly unless the regulator lead can be separated and brought to the isolator). When the vehicle is being driven, alternators will easily produce the extra 0.3V to 1.0V dropped by the diodes. The charging current at idle speed will be reduced, sometimes significantly.

I don't like the isolators because voltage drop at high current produces heat, which eventually kills the diodes. Also, good grounds are very important to prevent starter pulses from popping isolator diodes. Sometimes isolators fail shorted, often they fail open.

I prefer a 50A (30A relays have been unreliable) aircraft or ambulance relay tied to the "RUN" lead for charging. The starting current back feed is reduced by using 12 gauge wire for the charge lead to the aux. battery. 12 gauge has plenty of copper for charging, but drops enough voltage under load to prevent damage to the deep cycle battery. If you were really concerned, it would be simple to interlock the relay with the start switch.

> Also, I recently read an old post from Bob Bergevin in Fritz's repair
> log about the inadvisability of connecting auxiliary lights through the
> truck's light switch.  He recommended using a relay. I'd like to know
> more about how to install such a setup to wire the running lights on my
> slide-in camper to the Ram.

If you have the tow package, grab the running light feed from the trailer harness.

If not, mount a 30A relay under the hood, feed it through a fuse that is connected to a convenient power feed (I have a terminal block that is fed directly from the battery). To switch the relay, splice into one of the parking light feeds, it is an 18 gauge black and yellow wire on the 94-96 models that goes to each park light and each marker light.

Run a 16 or 18 gauge wire from the relay to the camper lights (I used a 4 pin trailer connector between the truck and camper for lights, charge, ground, and CHMSL), run another wire of the same size from the battery ground to the camper ground.


Subject:     Dual battery installation -> FINISHED !
From:        "Tim B"

 finished my dual battery installation.  I got a nice solid state isolator/combiner that has minimal voltage drop from Hellroaring Technologies.  There web address is  They have two models of isolators/combiners.  I got the BIC-75300 and it was $139.95 plus shipping.  This unit (BIC-75300) is pretty nice and is state of the art.  I have my second battery (Optima red top starting battery) installed in the backup starting role with an Optima yellow top (deep cycle) as my main battery.  The Optima yellow top has 750 cold cranking amps which is plenty for a starting application with the added benefits of a deep cycle.  I have a three way switch and LED mounted in the headlight switch plate that allows me to turn the unit on, leave it on automatic, or off.  The LED lets me know if the unit is on, meaning that the backup battery is combined with the main circuit/main battery.  In automatic mode (normally where you leave it), the unit comes on (combines) only when a charge voltage is detected on the main line (> 13.4 volts).  The main battery can be drained by leaving the lights on or even removed.  I then can press the rocker switch to on, the unit switches on, and I can crank through it to start the vehicle without every popping the hood! Very nice.  The only down side to this unit is that it isolates in only one direction so you shouldn't hook up any accessories to the secondary battery as you could drain both dead even if the unit is off.  If you don't want to be able to crank through it you can have it isolate in both directions.  It has a few different ways it can be hooked up.  Routing the 2 gauge wire to the starter was the only tricky part (and finding someone to fab some 2 gauge cables).

I am not affiliated with Hellroaring in any way, I'm just a satisfied customer.  Mike is the main guy there and customer service is good.     '96 Ram 1500

Subject:    2nd Battery for Camper
From:       "Tim B" <>  

I just finished a 2 battery install on my 1500 V8.  I have a nice solid state isolator that has almost zero voltage drop when active, and has current in-rush limiting built in to avoid blowing a circuit.  Check out Hellroaring Technologies  for the BIC-75300.

I set mine up so my second battery is a standard starting battery and is charged by the alternator but isolated from the main battery.  My main battery is now a deep cycle with good CCA (Optima yellow top).  This way I don't have to rewire anything.  In this configuration you could tap your power wire on the 7 wire trailer connector and be using your main battery. If you happen to drain it dead, just flip a switch inside the truck and crank from the backup battery and off you go!  The only drawback to this device is it's $140 price tag.  So far, I think it was worth it.

Tim B

From the Hellroaring FAQ Page:

Q: I'm concerned about not obtaining full charge efficiently due to diode isolator voltage drop.
     Does either of the Hellroaring isolators have this effect?

A: No.   Both of the Hellroaring BIC-75150 and BIC-75300 isolators use solid state switching
    technology, not just simple diodes.   When your auxiliary battery reaches full charge, you can
    expect less than a 0.005 Volt drop!    It is often less than the voltage drop across the wiring
    used to connect it!    On our test vehicle, a 4x4 suburban, the voltage drop at full charge
    measured about 0.001 Volt across a BIC-75150.   See No diode effect!


Subject:     2nd battery for a camper
From:        Bill Kerr <>

The 2nd battery lives in the back of the pickup box when the camper is loaded; my camper doesn't have a permanent location for a battery.  The 2nd battery is charged through a continuous duty solenoid (available at camper supply stores) that is switched from inside the truck.  I chose this path rather than use the 7 pin trailer connector because I often tow something when the camper is on the truck.  I took others advice and installed a relay to power the clearance lights on the camper.  Again, others suggested using the trailer harness because the taillights are powered through a relay in the harness rather than through the headlight switch.

Some people use isolators and I had one installed on my last truck, but it had a much lower capacity alternator.  Isolators of the 130 amp variety are expensive and seem to be more prone to failure than a $20 (Cdn) solenoid.  The thing I like about the switched solenoid is it gives you little more control over when the auxiliary battery is being charged.  The camper place recommended switching the solenoid from any source the is hot when the ignition key is in the "on" position.  I didn't like that idea because should your camper battery be seriously discharged, as soon as you turn your key the main vehicle battery is being drained by the camper battery.  This way you get your truck running, THEN switch on the charge circuit for the camper battery.



Last update: September 17, 1999