"Eric Greenwell" wrote in message
...
It sounds like you are effectively doing an internal resistance measurement.
Exactly. I find that internal resistance is a great measure of the health
of a battery.

Do you have chart of volt drop, load, and good/ok/bad decision for various size
batteries?
No, but I usually consider any drop over a volt or so to be suspect
(assuming an appropriate load for the size of battery). In my work, I often
have the advantage of having identical batteries to compare against each other.

I've not seen that sort of thing in battery data sheets, so I assume you have
to develop the numbers empirically.

True, but for auto-sized batteries the tester I mention (a very common
type) comes with markings that make a great starting point.

Vaughn