I have one APC SUA1000 XL usb . I got it some years back , that financially i has in better shape . This UPS because of the XL logo , uses two batteries of 12V 18Ah its one , also the same battery can be found as 12V 17Ah . Its in total one 24V source . The APC XL devices , can use also external power pack of batteries , in my model i can use ten of them. That sum of ten power packs, can keep alive one loaded system for about 32 hours on battery. End of the prologue .. My main battery pack called as RBC7 , the smart APC corp , have in the UPS software, one pest , that notify it , if the customer has need for replacement battery , and the mail spam starts automatically . APC has tremendous high prices , and for my model the prices float around 150 - 170 EUR . Equal or better ones ( Panasonic 10 years longevity ) can be found from 80 - 100 EUR . Currently , as my main pack failed , i use two smaller ones in line , 12V 7Ah the common type found in many or all small UPS systems . I have a minimum run time of 14 minutes or so , and the UPS software fails to finish the run time calculating test ( APC probably has a fixed amount of time so to report good news, at lower from it , you get multiple nags on your event log ) . Any way , i am looking for other options , car batteries or you name it . If you have something in mind , let me know .. The large run time , its not what i am looking at , even if the 57 minutes run time that this UPS offer as new device , it is sweet . .