U3

B.B. Battery SH4.5-12
12V,18WPC
15mn/1.30VPC

http://www.gearhack.com/myink/ViewPage.php?file=docs/CyberPower%20425VA%20CPS425SL%20UPS%20Disassembly

https://www.amazon.com/gp/product/B00K8MYSWG?ie=UTF8&tag=gearhack-20&linkCode=as2&camp=1789&creative=9325&creativeASIN=B00K8MYSWG

https://www.amazon.com/Battery-replaces-4-5ah-SH4-5-12-4-5-12/dp/B00BSEK3OA/ref=pd_sbs_23_1?_encoding=UTF8&pd_rd_i=B00BSEK3OA&pd_rd_r=2496ZFZW0W0JMGJJ695Z&pd_rd_w=qa7gV&pd_rd_wg=QRIn1&psc=1&refRID=2496ZFZW0W0JMGJJ695Z&dpID=518qQMx2OaL&preST=_SY300_QL70_&dpSrc=detail

NOTE: Online the 425VA looks different, with a different battery