Yes, you can use any USB charger as long as it is 5v. MicroGen has circuitry inside to protect the battery and ensure it is charged correctly. Thus, the battery will not be damaged.
Note: If the battery charge indicator is not calibrated, it is not being fully charged, even though it indicates that it is. Please leave it on for over 5 hours, even if it is indicating full charge. After 5 hours, MicroGen automatically calibrates.