Kindle 3 Replacement Battery

Have been having recharging issues with my two yr old Kindle 3.  Just fully charged it used for 1/2 hour, turned off and when turned back on a few minutes later would not come on.  Sliding the power switch about a dozen times may result in the green light coming on but light goes off as soon as button is released and nothing happens.  I have seen videos about replacing the internal battery.  Is this safe and can I buy one from Amazon versus a third party vendor?  Thanks