Just enough to fill your tires. It's easy to use, but the instructions are incomplete. You can tell the person who wrote them didn't speak English well. The main problem is the battery life. If it is not left plugged in, the battery in the case will discharge. The seller seems to be aware of this and even sent an email asking them to contact him about a new design battery. I only did this to learn that in order to get a new battery I have to write a positive review and give it 5 stars. No Deal - If you want 5 stars, sell a product free of defects. A good lithium-ion battery will retain its charge over a long period of time when stored. This is a decent product on a junk battery.