This product heats up when connected to a battery, warming the bento box placed inside. It's just the right size for warming small convenience store bento boxes and drinks. Around this time of year, if you connect it to a battery about 2 hours before you plan to eat, it should be ready to eat. (This is assuming it will be left in the car.) It also has a pocket on the back to hold the battery, making it easier to handle than you might expect. The battery is not included, but any battery with an output of 5V2A or higher can be used.