The best way to ensure that the battery does not get depleted is to remove it entirely from the PowerShell™ and store it separately after it has been fully charged. There is no way to turn off the flow of charge from the battery to the Z1™ or Z2™ if they are both in the PowerShell™ together.
Additionally, the PowerShell™ itself will draw a small amount of charge from the battery and drain it within 2-3 days.
We suggest that, to maintain a charge, your battery be fully charged every few weeks if you are not using it on a regular basis.
Note: Make sure that your battery is fully charged before disconnecting it from the PowerShell™. When you have 4 solid bars that are no longer flashing, the battery is 100% charged.