you can have the 505 battery info here:
http://www.batteryship.com/htmlos/ht...Reader+PRS-505
the model type is 323450-A7T, cost about 5 US$ in China. Following is an working instruction of battery replacement (with pics), sorry it's in Chinese
http://www.hi-pda.com/forum/viewthre...&extra=&page=1