If the unit in question is a Dyson Cordless Vaccuum, check the voltage that your wall charger is outputting. To do this, use you DVM Digital Volt Meter and set it to 200 DC VOLTS. With the probes of the meter, you should receive a reading of 21.6 DCV or a volt or two more, maybe even as high as 26 DCV but not below 21.6 DCV. This will indicate proper working order.