a lot of varibles but......

[Piotrsko]

Doubling is twice as good and half as dangerous However, to increase wire gauge size you need 4.

Realize I am spitballing based on I really don't know how much actual you'll see but I dislike dash fires intensely. I observed Some young lady plug a lipo boost starter pack into her cigarette lighter with some awful tiny chinese wiring then lived to drive off when it started.

[aerohead]

I lost an alternator 1,500-miles from home. It was a weekend. I might have waited days for a part, at $100/day for a motel room.
A casino courtesy bus took me to the local Wal Mart. I bought a battery charger and a spare battery. Charged the original battery overnight.
Left for home in the morning, driving constant loss only during daylight, until the ignition failed at around 500-miles. Swapped batteries and continued on until dusk, then grabbed another motel room. Rinse and repeat.
Made the trip home with no alternator.
So, for me and the T-100, it was about 500-miles on a battery.

[redpoint5]

It's not really the miles that drain the battery, but just the ignition being on. In other words, you tend to get a certain number of hours on a battery charge, and you could spend those hours idling in traffic, or screaming down the freeway.

Dad lost an alternator in CA (I-5 south) in the van and we coasted into a rest stop. Someone was willing to put jumper cables on long enough to get enough of a charge that we made it to a parts store where my dad replaced the alternator.

[freebeard]

This is why you want a diesel with a hand-crank starter. Maybe a mainspring with a winding crank.

[redpoint5]

It's why I bring an electric unicycle with 25 mile range with me on trips, and a few basic tools... and a 12v battery jump pack.

If I lost my alternator, I'd hook up the boost pack and continue on.

[Nathan jones]

I'm sure multiple smaller 12's would last longer, 5 or 6 7.5 sla's?. A new alternator would be easier especially at night

[porgies]

Heres what ive done, please tell me what you think. the extra battery is behind the driver seat. i grounded it via the seat frame and run a 4 conductor #12 wire to the main battery in the engine compt. I did find an old switch from one of those power pacts that i can shut off the second battery at iny time, i hve and will not use the cig plug for charging but the circuit that i have used for years, the only difference is now the array is charging two batteries instead of one, thx for your time, porgie

[Isaac Zachary]

Originally Posted by porgies

Heres what ive done, please tell me what you think. the extra battery is behind the driver seat. i grounded it via the seat frame and run a 4 conductor #12 wire to the main battery in the engine compt. I did find an old switch from one of those power pacts that i can shut off the second battery at iny time, i hve and will not use the cig plug for charging but the circuit that i have used for years, the only difference is now the array is charging two batteries instead of one, thx for your time, porgie

Sounds good to me. I'd just shut off the second battery during starting as 4 x 12gauge wires may be good enough for everything except starting currents.

Also, just in case you didn't know this, although you probably do, use the same amount of wires to the ground. (I knew a guy that would run thin wires to ground and negative and fat wires to possitive thinking that power only ran through the possitive wires.)

[redpoint5]

There's a fuse somewhere in there too, right?

[porgies]

Thanks for all the input and the system is up and working, the one mod i do want to add is fuse the second battery, ive found a 50 amp fuse that looks like it was one of those teenager high performance stereo speaker system. The fuse holder is approx 4 mm dia wire so that should be 7 awg ( right?)
So now im wanting to hook this up to my bat to bat + link that is 4x #12 wire. Is that fuse too large for the 4x12 wire and if not it should be as close to the main battery ??? right.
Thanks again for all the hints, helps, comments, and stories....porgie