Plug the device to a charger. The lights should come on as expected, and, depending on the battery chemistry and capacity, should show the charge process as expected.

When the charge shows as complete, unplug, attach the dust collector, and start the engine.

Start a timer and let the vacuum run for a while to make sure it doesn't turn off, overheat, or catch fire (unlikely).

The user manual states a run time of 14 minutes on a full charge. It is recommended to supervise the running of the vacuum for at least this amount of time.

Ideally, let it run until fully discharged. When empty - stop the timer.

Hopefully the new run time is much longer than the old batteries. In my case, it was 24 minutes vs ~5 minutes on the old and used batteries.

It is normal for the body of the vacuum, the handle specifically, to become warm to the touch during operation. However, even when run for 24 minutes, it should not become hot, nor should there be any melted plastic smells