Store backup device charged or drained battery?

[bghill]

Got a new eleaf 50W the other day. I plan to make this my main device and keep the iTaste MVP2 as the backup. I don't need it to be "ready to go at any minute", just as a go to in case the eleaf dies. ie: I can always wait for it to charge if storing it dead is best.
Should I store this fully charged, partially charged or not at all?

 

[WillyZee]

around 1/2 full

 

[Thrasher]

+1,..............

 

[bghill]

Will do it that way.

Thanks