Responding to comment 10... I'm using three 3.3volt sensors that need a steady 3.3v.(from what I remember the data sheet says) And from other answers regarding the solar I think I'll just charge by minight USB.
Thanks to MarkT for the diode suggestion.
I've also thought about using two batteries to make 7.4vdc and then using a voltage regulator. I know it will drain the battery a little faster. But in reality I only need it to run for 4 hours tops before recharging
I'm just looking for suggestions before I actually start doing anything on this project.
As far as protection goes I'll be using over charge protectors and the batteries I have looked at do have discharge protection built in.