Reason ? Does this car have anything besides the starter and ignition to supply? Lights ? Radio ?
Before you can look for a small battery you need to know what the total current demand is in the system.
If you have a good engine that starts easy and a new starter and cables you can use a riding lawn mower battery. A friend hollowed out a original green cap battery and put a lawn mower battery underneath. It starts his Cuda to get him from the trailer to the show.
A buddy of mine has a Braille AGM battery in a Mustang. The battery weighs under 7 lbs and works for some occasional street cruising. I think he told me it has over 200 CCA. Enough to start a blown 428 anyway...
There are lawnmower size batteries used in the aircraft industry. Lots of grunt.
Buddy gave me one that time-x’d. At least he didnt want to be let down at his rice lake.
I have one of these for my motorcycle. I hooked it to my hemi ram and it will start it.
Weighs around 2 pounds. Now I doubt it would crank a high compression engine but damn these things are powerful for their size. Also they will hold a charge forever. Pulse 3 Lightweight Motorcycle Batteries | Full Spectrum Power
The key for You is not the current output, there are a lot of modern batteries that are very compact with the balls to turn over a slanty, it's the reserve capacity that You may need on a smokin' hot day and it doesn't want to start for fuel related issues,or if You're starting it for some reason in the middle of winter at sub-zero temps. Reserve Capacity numbers are what You want to compare......
There is a youtube video if a guy who made a super-capacitor and was able to start his car with it...not really practical unless you got a perfect tune EFI motor that starts every time in under 5 seconds and an alternator that can more than keep up with all your car demands at all RPMs
The small scooter/power wheels batteries you see at walmart with the straight spade connectors are ~12V-10Ah. A Mopar Nippondenso starter usually draws 125-250A, and is rated at 1.4Kw (1.9HP). 1.4Kw/12V =116A. The hand held "battery jumper" things you can carry out to your car when its dead usually carries 2 of these in parallel for a theoretical 230A potential. It is noted that the jump packs do say to limit the starter to 8-10 seconds with a cool down period of up to 3 minutes between cycles. The cable are usually smaller and do heat up. They have some insane jump boxes out there now. 600A out of a 18Ah battery? And all this under 1lb and fits in your glove box.....WOW! https://www.amazon.com/dp/B01D42TYFC/?tag=joeychgo-20
BONUS>>> it has all kinds of power taps on it for USB, phone, DC jack outs, etc. pretty friggin cool.....
Thanks for all the replies. Stock 71 slant in a 62 lance r with nothing extra. Will be going with small turbo later. Don't want anything expensive. I used to use a small tractor battery in my 88 Daytona, turbo ,itnever had a problem. Just trying to save weight any weigh I can.
That's funny. I was thinking about when I first saw this post several days ago that I would connect 9 AA batteries together to get 13.5V. Then see if my 225 slant would start. When warm, you can hardly hear the starter spin because it fires right away.
Same principle with 2 lighter plugs on a 20 foot cord. plug into the car next to you and wait 10 minutes.....Or just carry a small dedicate emergency 12V battery in the trunk...next to that extra ballast resistor...