What is it???

[BuffaloJohn]

Thank you everyone. I think you are on the right track. I wonder if I could use it to measure the current in a 12v lead acid battery? The battery charges to 13.6v but doesn’t seem to have any current capacity. I have a Simpson 372 ohm meter and a Fluke clamp multimeter.

If you know the resistance of the shunt, you can measure the voltage across the shunt and derive the current:

V=I * R

If you have two, you can calculate the third.

In looking at the Simpson 372 ohm meter specs, I see that you should be able to measure down to fractions of an ohm, but I couldn't find any specs other that +/-3% of full scale and this being the low end of a 2 decade log scale, short of having reference resistors, I don't have a clue if it would work. If it were me, I would stick to voltages, those meters generally have more digits and a better chance at getting enough resolution.

But, you asked about a 12v battery that doesn't have any current capacity. 13.6 is the float level of a 12v wet cell lead acid battery but charged it should get above 14v. If your charger can't get it higher than 13.6v (you can put a voltmeter on a charging batter and it won't harm anything - neither charger nor battery nor meter), tHen you charger might be shot. If it charges to above 14v and then quickly drops after the charger is removed, that is usaully a bad battery.

If it should have much more current, then it is possible the battery is almost dead (internal resistance, internal bridging, broken plate(s), electrolyte problems, and on and on), but without much more detail... This is not a case where Miracle Max can revive the battery with a magic pill:

Could you measure the current capacity of the battery with this device? Probably. To do so, you need a load and the shunt and the voltmeter.

I would take the battery to a battery store and have them test it...