Lot no 90636  $18.  They say 100 amp 6 and 12 volt.

The best battery load tester available is your own dome light and starter.

What do you want to test it for? Leaks? Coolant strength?

Why spend any money, you have a load tester.  Turn on your headlights
and watch the battery voltage.  A good battery should be able to power
your headlights for 1/2 hour before the voltage drops below 11 volts.
Don't discharge the battery below 11 volts, you risk damaging a cell
by reverse charging it.  You might want to have a battery charger
handy incase you can't start the car after the test.

You might also consider the fact that you can't do a load test on a
battery that isn't charged.

Jack

I'm pretty sure that the Harbor Freight battery load tester would work,
however, I doubt if it would get much use.  I got mine from my dad, and as
far as I know, it hasn't been used in 40+ years, and that is with me fixing
most of my friends' cars.    A volt meter, the car's headlights, and the age
of the battery are what I use when deciding whether or not to replace a
battery.

Most places that sell batteries will load test your battery for free.

Radiator testers usually come in kits so you can check the cap and
pressurize the radiator.  Caps are inexpensive enough that when in doubt, I
just recommend replacing it, especially if it is over 10 years old.  I am
not a fan of pressure testing old radiators because the pressure test itself
can make an old radiator leak because the pressure test can be more than the
pressure developed by the cooling system.   Bottom line, a cooling system
tester is probably not worth the money unless you intend to work on a lot of
old cars.

 I have one (not sure if it's the exact same one...) used it a few
times - it's useful as an easy "Go/No Go" test of the battery, don't
expect any precision out of it.

 When I used it, I hooked up my known accurate Fluke DVM across the
battery posts to make sure I was getting an accurate voltage reading
out of the HF tester, and the mechanical gauge movement was close
enough for gummint work.

 I'm still in the "When in doubt, get a new battery - they're both
perishable and relatively cheap" school, but it's nice to know it's
really bad before you condemn it.

     --<< Bruce >>--

Is anything HF sells any good?

Yes, sort of.
The HF tool claims to be a 100 amp load.  If your battery were
for example a 600 CCA battery, the proper load test would be 300
amps  (CCA X .5 or amp hour X3) for 15 seconds, battery voltage
not to drop below 9.6 volts during load.
Since the HF tool only applies a 100 amp load, you'd need to
increase the load test time from 15 seconds to 45 seconds to
obtain the same results as a real carbon pile that can apply a
300 amp load.
Headlamps that draw 10 amps left on for 450 seconds would achieve
the same results also.

Transconductance testers are much more accurate and capable of
finding a battery with potential problems, they also have the
advantage that the battery needn't be fully charged to obtain
accurate results.

Yes.  Snap-On, Mac, Matco, Cornwall and many on-line tool vendors
sell the correct adaptor.
Price; I'd guess between $30 and $50
There are threaded styles and bayonet styles so choose carefully.