I purchased a 3.7V cellular battery from an Amazon supplier a few months ago. Red = positive and black = ground, correct? Sure. A couple weeks afterward the company threw away an $85 modem board. Cause of failure: the battery leads had reversed polarity.
A few days ago I took receipt of a solar panel from one of our suppliers.
Colors match on the multimeter probes with the colors on the wires, but the voltage is negative.
Now the colors mismatch and the voltage is positive….
Fortunately the positive black wire plugs into the slot labeled “+” and the negative red wire into the slot labeled “-“, so nothing should be damaged. But just to be safe I will contact our supplier and discuss the concern before I plug in a rechargeable battery–a battery that I also polarity checked.