If you have still got the old Logitech LX700 cordless mouse (Ihave and its still going strong) you can get replacement 1800mAh batteries at Batterytrader.com
Logitech LX700 battery
Hi There
you can get the logitech G7 battery replacement at batterytrader.com, here is the link
http://www.batterytrader.com/logitech-laser-cordless-mouse-831409-831410-1903101000-nta2319-lll11-battery-replacement-p-19607.html