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`Aux. Battery?

I'm planning to add a Auto battery to my rig. I have several questions; whether or not, must you remove the motorcycle battery, if you add a auto battery? If the motorcycle battery can be kept, will the charging system on an 81 goldwing 1100 I, be able to charge both batteries? Will it be necessary to put the Auto battery on an isolater, because of the AMP copacity of the different batteries. Its not that I want to use the auto battery to start the motor, although it would be good as a back up, it will be used more for auxillary items, like a laptop computor, Aux lamp for those unscheduled repair stops at night, and possibly to power aux. oxygen equiptment for my personal needs, etc.....

Jim ,It's possible to hook both batteries in line, but I just removed my bike battery and installed a big auto battery in my right saddlebag.
lot easier,just extend the csbles to the auto battery. the big car battery is more than enough to run your accessories, AND start your bike fine.
the bike altenator will charge the auto battery just fine, if it is reasonably charged to begin with. the Alt will replace the amount used as it normally does. Idoesnt make any difference how big it is.
like in an auto, dont try and recharge an almost dead, or very low Battery with your alternator.
I hot wired in a Battery tender, to the battery cables, where the old battery was, to be used on occaision when the auto battery is low.
if the bike sits for weeks in your garage, just plug it in to keep it topped off.[no need for it yet on my /5]
you [I] can also plug it in at a campground if needed, overnight, to top it off.
just one battery to worry about. nice!!
also, a dividend is If I ever have to remove the SC from the bike, the battery stays with the bike, in the saddlebag.

I'm in the process of wiring a second battery for a piece of medical equipment. I'll be keeping the original to make sure the bike will start in the morning. In the past I've done this with camping trailers and never had a problem with different sized batteries. I've never done it with batteries as different as a car battery and an MC one, though.
To do this, pick up an $8 starter solenoid for a 1960 to 1987 Ford pickup. Photo Sharing and Video Hosting at Photobucket attach a 10 gauge or heavier wire from the second battery positive to one large stud and a wire from the main battery positive to the other large stud. Now attach a 16 gauge wire from the small terminal (Marked I) to any wire that is hot only when the key is on. When the ignition is off, you can drain the big battery without affecting the original, but when the key is on, both batteries will charge.

Now for the disclaimer. I have never done this on anything new enough to have computerized ignition circuits. The newest vehicle was a 1994 Suburban. Let some of our electronics minded members speak up before you take my advice seriously.

Here's a diagram I found that is much neater than one I would draw. The only difference here is that they are drawing a trigger from the alternator while we did it from the ignition. If you wish to buy a factory made isolator, this diagram came from

Photo Sharing and Video Hosting at Photobucket

Bob in Wis. What make and model of battery are you using, to put in your saddle bag? What are its reserve cranking AMPS? I have the Honda Line, hard saddle bags and most auto batteries I have seen, appear to be to wide to fit into the them. If I had to buy a narrow enough battery, that didn't offer adiquate reserve cranking AMPS, I don't think I would want to buy such a battery just so it fits.

I bought the battery at our local Fleet Farm store. it is a 550 CCA battery.
compared to the 28 AH stock battery.
9" long and 5" wide, and 9" high..made for some small import car.
I have one in my /5 with R100RS engine for 2 years, and now the same kind of battery in my new 85 K100 bike.
I can run camp lights, air compressor, off it with no problems staring the bike later.
measure your bag opening and visit the local store, and see whats available. lot of odd sizes now for various imports.
the foam I inserted to keep the battery from moving around. also put a layer on the bottom, with a hard rubber pad along with it.
the small tupperware box fills in extra space, used for small articles...bungie cords in my case.

Mike, could i get a copy for the Aux Battery hook up ?

Thanks Mike,


We have run just a car battery with our own rigs for years. Thye last forever and cost less. Never saw any reason to try and compolicate things by retaining the motorcycle battery.
Car batteries cost less, last longer, can be used for ballast if placed in the right spot, can take a quick charge if necessary and have the capacity to run many accessories off of when camping. The motorcycle charging system will do fine with them unless they are drained down too far. Due to the concern with this it doesn't hurt to carry a charger of sometype when camping.
I prefer to mount the battery in it's own box, Have placed them between sidecar and bike, inside the sidecar and also behind the sidecar wheel (best weight distibution here). Have also wired in a conventional recepticle on some to allow camp lights to be plugged in. Any 110v light can be used if the bulb is replaced with a 12v unit.

Note that if th ebike battery is to be retained it and the car battery need to be rigged so they can will be chareged seperately if the bike's charging system is to be used. Trying to make them charge on th esame circuit is asking for trouble due to the difference in sizes.

To me car batteries are THE way to go with any sidecar rig. Keep it simple and have fun.

Yup, like Claude says...ther is no reason to keep the original bike battery in the system. just extend the cables and install the car battery. plenty of startup power left even after all night use in a campground.
all you need extra is a battery tender to top off the car battery if it is low.

Time to jump start this old thread...

On a KLR650 rig, mounted a lithium 420CCA battery on the sidecar eliminating the OEM biker battery. Now after installing a separate fuse block for the many auxiliary outlets, LED driving lights, charging port for laptop and camera, air horn, etc, am having a small voltage drain somewhere in the aux wiring. Then installed a 30A switch between the battery and the auxiliary fuse block so I can turn off all of those circuits when am off the bike.

Since I still have the original bike battery, am thinking to reinstall it with a diode isolater between the two batteries. It would first charge the bike battery and when full, charge the sidecar battery. Will have the OEM battery for starting only and the sidecar battery for the auxiliary items. If the sidecar battery is run down, will still have the fully charged bike battery for starting.

Above they mentioned going to one car battery, but since I already have both batteries, the only additional expense is the isolater and some wiring. Where I am most concerned about needing this, there will be no outlets for plugging in a battery tender.

Any recommendations on which isolater to use? Or suggestions/comments?

I'd stay away from diodes, and go to a VSR (voltage sensing relay, either solid state or a physical latching relay).

Fewer system losses due to heat, and you don't need to horse around with the regulator to account for the roughly 0.4vdc drop across the diode.

Either a chandlery or an RV shop will have them.