I have an APC Smart-UPS 3000 XL battery backup. In addition to the internal batteries, it has a connector for adding an external battery pack to it. While it's available on Newegg for WAY cheaper ...

Under the "APC Smart-UPS Tower" category (the consensus recommendation for price/performance it would seem), there are only 750VA, 1000VA and 2x 1000VA units available.

The battery can be removed by popping out the front panel and unscrewing a cover plate. Included in the APC Smart-UPS 1500 is the APC RBC7 battery, which is a set of two 12V, 18.0AH maintenance ...