DIYbanter - View Single Post - What is the proper way to test alkaline batteries?

mike[_22_]

On 9/22/2017 6:06 AM, wrote:
On Thursday, September 21, 2017 at 7:46:39 AM UTC-4, John-Del wrote:
On Thursday, September 21, 2017 at 3:35:43 AM UTC-4, GS wrote:
Phil Allison wrote:
GS wrote:

--------------------
Phil Allison

** The ESR of a cell or battery is a good guide to its condition.

A fresh AA alkaline measures 0.1 ohms or lower while a tired one
measures 1 ohm or greater, a fresh 9V measures under 1 ohm. Along with a
voltage test you have enough info to match or discard used cells.

.... Phil

What's a good way to do that ?

** Do what ?

Test ESR or correlate it with open cct cell voltage?

.... Phil

ESR.

Greg

IIRC, you take the open circuit voltage and write it down.

You take a voltage reading under a known fixed load and write that down.

You plug those two voltage readings along with the load resistance

value into a formula (that I can't recall) and you get the internal
resistance of the battery.
Which voltage do you use?
When you apply the load, the voltage starts to drop.
So, which voltage along that curve do you use?
And when you "let go", the voltage won't return to the original level.
Note that the voltage at the instant you apply the load won't be available
unless you use a scope, or some otherwise accurate sampling to measure it.

Great in theory, but not nearly so simple in practice.

Waaaay too much trouble IMO. In recent years, I've found OC voltage sufficient to determine battery condition of basic alkaline cells. For high drain applications such as flash lights, anything at 1.5 is fine. For lower drain things like pocket radios or remote controls, anything above 1.3 works for many months. Any cell that reads 1.55 or above is virtually new.

Wow, too much trouble? It's just ohm's law.
Say V_O is open circuit voltage, V_L is with load R.
I = V_L/R
Bat_R = (V_O-V_L)/I
(The ESR may change with load current...
I don't know.)

George H.