I would like to get back to walking now that it's getting cooler (I hate the summer) I lost most of my baby weight but have gained about 10-15 back and feel so gross and uncomfortable. I had one previously when it first came out and I liked it. I was thinking of getting the charge 2? What does everyone like about it? Also I read a while back you can sent back your old fitbit for a credit? How does this work? Where is the credit good for?