Elec. start outboard battery size FYI

[over40pirate]

I bought an older 25 hp Yamaha, elec. start motor. Not wanting to carry a big 50# battery around, I tried a battery from my garden tractor ($19.95 and very light.
When it worked, I bought a new one. It's worked fine.

[mike d.]

My son did that also with a motor cycle battery! The thing you will find is that it won't last as long, because of the draw down strain, over time! His lasted about 7 months!, even with taking out and charging on a quality house charger!

[a64pilot]

There are there what amount to tiny LIFEPO motorcycle batteries now, that only weigh a couple of lbs, but easily start liter Superbikes, I had on in my Honda Blackbird, and now have one in my Husqvarna TE-450, both much harder to start than an outboard I would think.
There are many, this is meant just as an example only
Amazon.com: Battery Tender BTL09A120C Lithium Iron Phosphate Battery: Automotive