Unlimited numbers of batteries banks can be added to the UPS units however it is recommended to add a Battery Bank that has an internal charger (PSCEBB18CH or PSCEBB60CH) if large battery banks are added and fast charging is required. Usually these should be added as the second, third or fourth battery bank depending on your requirements. When these battery banks with chargers are added, it is possible to substantially increase the number of regular battery banks. The following battery banks have built-in chargers. These also have more batteries than regular battery banks. PSCEBB18CH - Suits 2k & 3K, PSCEBB60CH - Suits 6k & 10K