I can find videos of 18 and 14.4 volt DeWalts hooked up to car batteries. Why does it not work with my 12 volt?
not any details to give, followed various instructions that end in nothing happening

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Steve
I have a circular saw too that uses the same batteries and I tried to use this wall wart (instead of my bigger power supply) and it doesn't work, but it still works with the battery. I wonder if there's a minimum amperage to activate the circuit so you can't run the battery to a truly dead state.
Replace NmiH about £25 Replacement 2 x 12v 25 Ahr lead acid £4.60