Is the battery replacable?
Can the rechargeable battery be replaced when it no longer holds a charge?
How many times can it be charged?
How often does it need to be charged?
No I don't think it does. I need to charge mine every 3-4 days, depending on how often I sync via BT to my phone. I'be been using a fitbit for 1.5 years and have not seen any deterioration in the duration of the charge. most rechargables say you can recharge "hundreds" of times.