On my Xperia X10, I flash ROMs weekly, sometimes daily. I use xRecovery and erase battery stats every time I flash. (As well as wiping SYSTEM, CACHE and DALVIK Cache). Battery life is just fine.
XBox 360 S, 16GB iPhone 4S, iPod Classic 160 GB, Dell Inspiron Mini 1018; Macs: Mac Mini 2.4 GHz 6 GB RAM; Macbook 2.0 GHz 3 GB RAM; MacBook Air 11", 24" Cinema Display