DSK writes:

Think of that 50-pound trolling battery as a gas tank that holds (the
equivalent energy of) a pint of fuel, takes all day to "fill"
(recharge), costs $$$, and wears out in a few years.

And the power equivalent is much more than
a pint of gasoline, especially if you factor in the woeful
inefficiency of internal combustion engines.

Nope. Here's the analysis:

My Group-27 deep-cycle trolling battery weighs 53 lbs and provides 115
Ah x 12 volts = 1.4 KWh. Divide by 746 watts/hp and multiply by 80
percent trolling motor efficiency, you get about 1.5 hp-hours at the
prop, from a full charge to full discharge.

How much gasoline is 1.5 hp-hours?

My 25 hp Tohatsu burns about 2 gal/hour. So 2 gals for 25 hp-hour, or
12.5 hp-hour/gal, or 0.08 gal/hp-hour, times 1.5 hp-hours, is 0.12 gal,
which is to say,

1 GROUP 27 TROLLING BATTERY = 1 PINT GASOLINE

Gasoline has over 50 TIMES the energy density of lead storage batteries.

A plain old lead-acid battery
can easily run thousands of charge-discharge cycles if it's
treated properly.

Huh? They're good for about 200 cycles, assuming you can log that many
before 3 or 4 years of aging works its harm. Then they degrade rapidly,
holding less charge, and self-discharging faster. Think of it as a gas
tank that starts shrinking and leaking after a few hundred fills, or a
few years of just getting old.

Unless you mean by "treated properly" that you don't fully discharge, in
which case, your realized energy density is even less favorable.