Check the Navspark forum - plenty of questions about power. http://www.navsparkforum.com.tw/viewtopic.php?f=23&t=195&p=760&hilit=power+consumption#p760 . Looks like a 700mAH battery is good for 8-12 hrs. For what it's worth my GPS module didn't have a sleep mode, so I used a mosfet transistor to turn the power to it on and off. Saves over 30mA when turned off 
Have you seen this one? May be of interest if you are thinking solar...