Battery replacement?

New to Forum so this may have been answered before but I’ve read this thread through and this brings up my question since buying my Sansa Fuze about three months ago.  With this type of battery how low should you let the power go before charging?  I know with some types of batteries it is better for the life of the battery to wait until it is pretty low before charging.  Is that the case here?  Thanks for your help and I have to tell you I am really happy with my Sansa Fuze I use it for audio books and have transfer 4 so far without any issues with the transfer or listening.  I love it.