Measure the voltage at the battery terminals with/without the charger connected. You should see a change in voltage. Let us know what this is.
Similarly, disconnect the batteries and measure the voltage at the wires (charger on) and let us know the result too.
Your 'new' changer may have been damaged by the old batteries and, after replacing the batteries for good ones, not be doing as it should.
There are other tests you can do that involve measuring the charging current but we'll come to that if you get back to us with the results from the tests I mention above.
The Israeli manufacturer's technical manager suggested that the XLR port was the issue. After considerable delay, they located and shipped a new port/harness, which I installed, but the batteries still do not charge. I don't believe the charger is the issue, as I had installed new batteries, then got a new charger, which lights up but does not indicate charging (fan doesn't run, LED light stays green all the time, and the scooter battery gauge does not indicate the batteries have charged up fully.
I tested the battery voltages: with charger turned off the voltages are 12.36 and 12.32 individually; and 24.7 tested together. With the charger on, the voltages are exactly the same, with no increasing voltages. I have seen videos of charger tests indicating if the voltages do not increase with the charger on, then the charger must be bad. However, there is no direct connection from the XLR port wiring to the batteries, and the charger power goes through the circuit board(s) and other wiring It seems to me that lack of charging with the charger on does not prove the charger is bad. Couldn't the fault be with a circuit board or in other wiring between the charger/port and the batteries?
Note that there is a resettable fuse which I reset with no effect. Also, note that the scooter does run and functions perfectly other than the batteries not charging. Also, with the charger connected and on, the throttle moves the scooter, and there is an inhibiter which is supposed to prevent the scooter from running if attached to the charger, so apparently the scooter electronics can't "see" that there's a charger plugged in.
Can someone offer any other suggestions for how to proceed? Thank you very much.