We have the same hand vacuum and it is a great unit. When the battery has run down it will stop and should be recharged. If you have totally done a good clean and nothing is in the rear vent, the filter is clean then it should run fine. However should it be a plugged filter and can not suck in it may overload the motor, drop the voltage and auto turn off. It has a setting to save the battery from trying to run when the battery is discharged so it will not ruin the battery. Ok with all this said the other reason would be a faulty battery, will not charge enough to run before it senses a lo battery. If your device is with in the warranty period they will replace the battery. There is no replacement battery part. The battery is actually several cells to add up to the voltage needed and a smart person could actually purchase batteries and solder them in for a repair.