HEPA filter recommend 3-6 month to replace according to the use situation health threats and hidden dangers Double click the power button to switch working mode ;sigle click the power button to switch wind speed mode it can not drive the purifier directly if battery out of power.means that the purifier motor have to drive via the battery . Battery can be charging via car usb (about 3 hours)or solar power (about 12 hours,depend on the sunlight intensity ) . please attention that the solar panel main function is assistance charging and extend the battery duration of use.