Car battery

You are correct. Some people claim you can run in to trouble if you ADD a car battery to the existing one, but there's no reason you can't replace the existing one with a bigger one.

I replaced my motorcycle battery with a small lawn mower battery from NAPA auto parts. I mounted it inside the saddle bag on my Honda Silverwing. It really helps on those cold mornings. I have had no problems for the year that I have been running it.

Go for it, Shoe..
better, faster starting, more reserve battery power for accessories.At the camp site I can run a camp lite, air compressor for my double air mattress,etc, and still have gobs of starting power when I need it.
a great plus is the extra ballast it will provide to the SC.
your bike alternator will not be overwhelmed by the larger battery.It will charge the car battery just fine, as it only needs to replace the small amount of amps used when the bike was off. same as the reg bike battery. It will top off the car battery just fine.
but...dont try and charge an almost dead car battery with your bike alt..it will be overtaxed.I have a battery tender wired permanent in the line to my car battery, just plug it in at the campground or motel over night if necessary. I havnt needed it yet in 4 years tho..more like a safety feature :o)
it HAS been on all winter in my garage, keeping the battery in a charged state.

It's a very good idea. Mind you don't get the cables too long. It would be good to have a nice large gauge for the cables if they are a bit longer than ordinary. It won't hurt a thing since the bike starting and light circuits can't use any more juice than the resistance will permit.

yes shoe,..I too added a 12 volt car battery to my existing battery and charging system,..to allow for the radio and DVD player,..I tied it in to the bike's charging system to keep it bumped up,..I used #10G wire in parallel series and load tested with a amp meter to check voltage/amp draw and drop to confirm the system & voltage regulator was not being taxed,...all was fine, just remember to not pound the starter for too long at one time as your excess reserves will melt internal wiring if allowed to over heat it.as your cold cranking amperage is greatly increased. good luck, crawf.

I put one in my sidecar, I made a Elc. chair lift and didn't want to take a chance on the bike battery getting low, I used 10ga and run it through a relay so that it will charge but when the bike is off so is it, that way if the bike batt did go south all I have to do is bypass the relay.
I strongly suggest that you use a AGM or sealed lead acid to elevate spillage, one battery to consider is a UBTZ14S, lots of CCA, AGM and it's small in size, just Google it and look for the best price because prices *really* vary for this Batt, it's used in a LOT of applications.

Well sirs,
I too think there shouldn't be a trouble to put in an autobatery instead of the bike battery. The regulator still will work with the same voltages and amps. The reloading will be a little slower but doesn't hurt to the battery, in fact it will help to make the bateries life longer (in a car in 3 to 10 minutes the starting draw is reloaded) the draw for a bike is something less so at the end the reloading wil be something like 5 to 15 minutes, so who cares?
By the way I had excellent results with a sealed NiCad batery out of a computer UPS. Lead bateries lasted only 2 1/2years to max 3 1/3 years and gave me trouble with chargeing systems. The UPS bateries seem to live longer without spilling acid. (the most astonishing case I saw was a Cadmium batery from the fifties that 1983 got its first charge after 17 years of beeing out of service. Its still running in the 1953 250 ccm Victoria/Steib rig)

But where I am concerned about is your wire gage recomendation that sounds preaty week to me. Test yourself. After haveing cranked the engine with the ignition off at least 5 seconds (engine kill button activated), how warm becomes your AWG gage 10 cable? Possibly more than handwarm 35ºC. that is a sign of too small cable.
I used car battery cable AWG gage 4 (same as welding cable) for 2*2m extension and even that got a little warm.
So I would go with gage at least 8, better gage 6 or 4 cable. Better don't use Household cable but car battery cable (beefy jumper cable), Welding electrode cable or if not available TSJ industrial cable, these are the cables with multiple filaments that are smooth to handle.

For Beemers and Guzzies the set up with an auto batery is specially usefull in winter, but your cooking equipement is still needed for to get the oil thin enough.
Anybody used for winter allready the modern sintetic multigrade oils here in the forum? I have seen a sintetic 5-45W that poored thin like cooking oil.

Best regards
Sven Peter

I have used jumper cables for auto battery connections but it is best just to get long battery cables with the ends already on them. You will never go wrong if the cable is too large gauge wise....no sense in messing aroung with small stuff just go for it.

I have #51 battery in the box on the frame between bike and sidecar.

HI:
After many folks said doing this was a mistake:
Put 1,000cca pickup truck battery in FSII trunk on our '95 GL1500[w/2 six ga. CU cables(black/red) approx. 2 1/2 ft. long to connect it]; ran with stock alternator 4 years. Battery developed bad cell 2 years ago. Replaced with 900cca battery; still doing fine[have ridden approx. 40,000 mi. since dumping stock Wing battery]. TTFN. Please Pray for our son in Iraq.....