I'm getting too old to pull-start my lawnmower.
I bought a used electric start, but the battery is shot.
A quality battery that actually has a specified internal
resistance is about $40. And even if I'm careful to keep it
charged over the winter, it's not likely to last more than
a couple of years. Depending on the source, it may have
been sitting on the shelf sulphating for years.

I went to Batteries+ and talked to the people.
I got lots of "consumer speak", but no actual
technical guidance. They're more interested in rotating
stock than selling me a battery with a recent manufacturing date.

The start surge current is 46 Amps, but settles to 15A or so
when cranking.

I have a bunch of old laptop batteries that I thought I'd
assemble into a starter battery. But even if I parallel
up enough cells, the protection circuit isn't likely to
tolerate that 46 amps. Then there's the charger...

There are lithium car jump starters for around the same
price as the lead acid. And that takes care of the protection
and charging and may have other uses beyond starting the
mower a few dozen times a year...looks like an option.

After some research, I realized that I don't know how they work.
Jump Starter specifications have gone the way of flashlight
brightness specifications. A typical EBAY listing has a
headline that says 20,000 mAh...but the fine print says
10,000 mAH...but it's in a package that might hold 2,000 mAH
of cells that are rated for 5% of the peak current required
to start a car.

If you sort the listings by price, you see page after page
of listings for ~$2, only to find that you get a cable for $2,
but if you select the battery, it's $89...or $2 plus $90
shipping.

I considered a cordless tool battery.
I have a 24V lithium drill battery with 6 18650 cells rated for 30A peak.
If I use 3 cells or parallel up 3x2=6 cells, I loose all the advantages
of protection and a working charger. And I'm thinking that 3-cells
may not be enough and 4 cells
in series might be a better option.

I'm seeking suggestions.
Maybe a pointer to a good value on a jump starter that may not
be crap.