On Fri, 12 Jul 2019 03:05:52 -0700 (PDT), wrote:

snip

Such a tool might be 'ok' for people who don't know how to use a DMM
as I'm not sure how useful most of the other things that you couldn't
do with a DMM are?


Internal battery resistance is key to starting ability & is a way to measure battery ageing.

Sure, but who would use that and when? 'Most people' just start their
cars until they don't start, then give it to a garage (or call their
breakdown service) and garages are likely to have better tools in any
case?

So you can use that to assess usefulness of out-of-car batteries.
Once fitted, cranking voltage is adequate to give some idea of startability, though it's no precise guide.

I have a discharge tester for that. Not a lot beats them for a RW
test. I also have a ACT capacity tester but rarely take any notice of
anything other than the capacity reading.

Some oldies give the battery a real hard time during starting, and some modern diesels require high cranking voltage to start at all.

Quite ... and if it no longer starts your car you get a new battery
[1] and this could be 35 quid towards it. ;-)

Cheers, T i m

[1] Or we would do some diagnostics with a DMM / battery charger
ourselves first (assuming no other tools). Cranking voltage, charging
voltage (on and off the vehicle) and even the charging time (from
supposedly flat) gives some big clues (as to the capacity).

p.s. Whenever I've tried to take a functional battery back within
warranty because of capacity loss, I've found it very hard to persuade
them that it is now way off what it should be. Basically, if it isn't
'faulty' they often consider it ok. I guess they might consider
capacity loss 'wear and tear' but it could also be some disconnected
plates, especially with sealed batteries when you can't see in each
cell.