From Sonic Retro
Chaos Drives (カオスドライブ) are small capsule-like objects with a coloured shard inside found in Sonic Adventure 2. They act as a power source to G.U.N. robots and are dropped when they're destroyed. Once collected, they can be used for raising Chao, adding to one of their stats. Additionally, for Tails and Eggman, a Chaos Drive will recover the same health as one ring does.