Hi, I have an old Macbook Pro from 2006 to act a server at a remote location, without me being around for a long time. This laptop doesn't have a battery and I want it to have one, just in case there is a power outage for a split second. My concerns are safety-related. I don't want it to catch fire after a prolonged period of time. I have a choice between: -a NEW NON-genuine battery on ebay -a USED GENUINE battery that only lasts 20 minutes Which of these options is the safest, given that the battery will never actually be used, since it will always be connected to the wall?