Maybe the output of the Aldi is defective ?
Do you have any other batteries you can test it on ?
If the Halford one can show it up like that, it sounds like more than just the battery at fault.
*******When measuring current with the multimeter, you have to plug the leads into different holes. There is a specific hole for current, to one side of the volts hole. Even if the meter is not powered, the shunt from "Current In" to "Common" will still be present and conducting.
--------X 20A COM X-------------- <=== in series with battery, | | NOT across battery! +---x- 0.01 ohm -x---+ Resistor stays ^ ^ in circuit, even | | if meter knob is +-- meter ---+ rotated. measures drop here
You can see in this sample schematic (for my meter), that the 0.01 ohm shunt is not switched out by the rotary knob.
Aldi ---- red --------X 20A COM X--------- Battery -------+ | | (+) (-) | +- 0.01ohm -+ | | Aldi --- black ---------------------------------------------+
You would also have to make sure the electrical connections are reliable, as some circuits, if the path was interrupted for only a short time, they would notice that.
Also, if you have *two* multimeters, you can use one multimeter on "ohms", to verify the current flow path from 20A to COM is "always on". Or, if you've blown the fuse, the second meter can tell you if the path is "always open" due to the fuse going on it.
I've known a few people to have blown the fuse on the ammeter part. Since I never ever use the ammeter holes on mine, they're mint :-) I use the clamp-on DC ammeter for safety reasons. The clamp-on has no duty cycle limit, for one thing. The clamp-on meter uses the magnetic field around the wire, as a proxy.
Two meters make great pals. Especially when they read consistently (agree on stuff).