I have a couple of hand held battery operated vacuums.

The internal brass charging contacts that are suppose to make
contact when the power switch is turned off will not always
conduct good enough to recharge the batteries. It is a bad design
that I have been unable to correct by modifying the contacts.

What I have been able to do is to wiggle the off switch every time
I need to recharge. This gives me the best shot at seating the
contacts.This has worked for the most part. The problem is that I
can not determine %100 of the time if the vacuum is actually charging.

Here's the question............The vacuum uses a low voltage
AC output brick power supply. Is there a way to make a add on
pickup/sensor for the brick or two conductor charging wire that
will let me know if the contacts are made and current is flowing?
I do not want to cut into the circuit.