The Autel MaxiScan OBDII scan tool requires no batteries and is easy to use. First - read the user manual as it is very good. After that, refer to your car's manual to find the location of your car's OBDII port (if you do not know where it is), plug the scanner in, then follow the user manual to use the scanner. This is a good scanner for cars built from 1996 on as cars since then have been required to have an OBDII port.If you lose your manual, one is available for download from various websites (just search for 'Autel MS300 manual') though the link on Autel's website seems to be broken at the moment. Still, a complete pdf copy of the manual was available in several other places.Before I plug the scanner into my car's port, I turn the car on to make sure that all accessories are turned off (radio, a/c, heater, fan, GPS, etc...) and then I turn the car back off. This ensures that there is no unexpected power variance from accessory use while the scanner does its thing. Then, with the engine OFF but your key in the ignition switch:* Plug in the scanner's OBDII cable into your car's OBDII port* Turn the ignition key only to engage the electrical system; do not turn to engage the car's starter* Press the Enter button (blue button on the left) and the unit will begin its scan* Once scanned, press the Scroll button (blue button on right) to see if the scan found any issues* If codes exist, the manual has a very detailed list of scan codes and description for you to reference* Turn the ignition key back to the off position, remove your key and remove the scanner's cable from your car's OBDII portThis scanner does not require any batteries to operate as it works from the power supplied by your car's battery via the OBDII port connection. It communicates with your car's central processing hub which collects information from the electronic control units of the major systems within your car (that is what the 'CAN Protocol' reference is about). However, to use it and to read results from it, the unit needs to be plugged into the OBDII port in your car... so you should keep some paper and pencil handy when using it.Our local dealership charges $80 just to plug their scanner into our car's OBDII and perform this diagnostic, so this Autel MaxiScan will save me that much each time that I need to use it. Additionally, I found the readout's black lettering to be easy to read against the backlit background,The last page of the users manual notes that this Autel MaxiScan device has a one year limited warranty, and that all warranty issues are handled directly with Autel through their website. If an issue arises before that period expires I will return here to update the review and let you know what the issue was and how resolution was handled. We did receive this product gratis from the seller and have put it through the paces to objectively find out how well it performed. My statements here reflect that testing.If you are looking for an OBDII scanner of this style and size, for use as I have described above, then I recommend this one highly based on its ease-of-use and excellent user manual.Go for it.