I got the Tennis Ball Charger 150 from Set US Tennis. I have been very happy with the result. The unit is equipped with a air valve on top so you can charge it with a compressor instead of the hand pump. It also comes with a special tool that allows you to tighten the cap so that it doesn't lose pressure over time. When I bought the device I had 144 Penn heavy duty balls about 2 weeks old which I use with a ball machine. I put the balls into the device and left them for 5 days and when I removed them they bounced just like new ones. There are only a couple of small negatives. The unit only holds about 140 balls, and you have to remove them manually rather than just dumping them out. It still only takes a couple of minutes. A little pricey at $300 but worth it in not having to fabricate something myself that may or may not work right. The benefit is saving money on balls and always having the correct bounce when I practice.