The Maestro has an INTERNAL battery that can discharge completely after a couple of months of not being connected to power. This is a serious issue as once it discharges it will not boot and needs to go back to the factory. Leaving the external battery in the unit seems to prolong the time you can store the Maestro without connecting it to power
HOWEVER. I would strongly recommend that you create a recurring calendar item to remind you to charge the Maestro at least every 60 days by connecting it to power. I actually have an Atomic Cobalt 2 Dive Computer which has the same internal battery discharge issue... So I calendar both my Maestro and Dive Computer to be recharged at the same time.