From reading what others have said, if running coils (decided this was the way to go rather than distributor as it's original plus sounds great) only on 12v battery, they say it's a good idea to bring a backup battery. Oh, and car will have no generator.
I was thinking, it would be much better to alternate between the 2 batteries rather than one remaining unused in the car.
Am I thinking correctly: the mag/battery dash switch (on my '24) could be connected to both batteries, thus run battery 1 on "mag" OR battery 2 on "battery"?
I'm no electrician, but the common sense approach tells me I don't know why you couldn't connect two separate batteries in the car, one through your bat switch position and one through your mag switch position.
And, perhaps if your second battery is only a emergency or back up battery, you could go with a motorcycle or riding lawnmower battery and save some space and weight.
Unless you plan on running with your headlights or some other amp sucking accessory on all of the time I think you would find that a single battery charged in the evening depending on usage would be more than sufficient. I ran my speedster for several years with a distributor, electric fuel pump, an electric starter and of course brake lights. I never found a need to recharge or switch batteries during the day and those days were often 200 or more miles. I would simply carry (or install) a voltmeter to monitor the charge level and recharge from day to day as needed. If you feel a need to have a belt with your suspenders, it wouldn't hurt to have a spare small 12 volt garden tractor or similar battery available but I expect you wouldn't need it.
The last guy, that I helped, had connected two batteries in parallel and he actually had less voltage at the starter terminal, while cranking, than he had with only one battery.
I disconnected one battery and measured the voltage while cranking. That was 4.8 volts.
Then I disconnected that battery and connected the other battery and measured the voltage while cranking. That was 3.4 volts.
One battery was actually trying to steal a charge while cranking.
With a new set of 2/0 ground, battery and starter cables, and the better battery, I measured 5.9 volts while cranking.
The engine started much better and quicker.
That was about 5 years ago and the one battery is still good.
I would definitely go with smaller lawn tractor type batteries. Carrying a hot spare isn't a bad option at all. Don't see the need for any elaborate/extra wiring either. Possible exception: a remote voltmeter to keep an eye on the battery in use just to let you know it's situation. Keep it simple.
Looks like you are right. I found this: http://www.funprojects.com/pdf/The%20Model%20T%20Ignition%20Coil%20-%20Part%201. pdf and it shows I can hook batteries up on either side of the mag/battery switch!
Thanks guys. I will be using smaller lawn tractor/motorcycle batteries.
I like to make sure when I am out in the middle of nowhere, and my coils are solely relying on a battery, I have a backup... just in case.
Whoops, Fig. 186.
Ive been thinking something similar for my engine ('14 no starter/generator/stock mag) What I will have is a cross drive mag setup that can be run as a dist or mag. Considering there is no impulse I may put in a very small bat just for cranking.
Here's more about batteries for a non-starter car. http://dauntlessgeezer.com/DG102.html
I've always used six volts, but from what I've read twelve is OK.
I've seen the same car run on 6 volts to the coils and 12 volts to the coils. At lower speeds, they both run about the same. At higher rpm, the 12 volts definitely made it run better. Seems to me there was a bunch of discussion on this issue some time ago.
Six volts is plenty to buzz the coils for starting. Presumably, at higher speeds you're running on MAG, which is much more than 12 volts. In that case the battery voltage is irrelevant.
OOooops! I just read the original post again. It specified no MAG. Yes, in that case I'd use twelve.
Thanks again, guys! And thanks for the link, Steve, that helps.
OK, while we're talking about the mag/battery switch, can anyone tell me the exact diameter of the HOLE OPENING for the ammeter: https://www.modeltford.com/i/c/474004l.jpg Not the diameter of the ammeter itself.
I run a T long while (all summer) on battery 12v
Without charging. (Small motorcycle battery )
Coils do no draw much I did run a brake light
I was going to use two lawn mower batteries one for coils and one for lights and horn.
I did carry an AA battery bicycle clip on light that blinks and flash if caught at dusk.
IT'S AMAZING HOW LONG A BATTERY WILL LAST NOT USING A STARTER
12v battery will not hurt coils
The T mag when set up right will produce much more