My phone can take a minute or two before showing data for time until charged. When I access that variable not plugged in it shows "-1" as described in the action info..
So, I would probably approach it by running the task, then using a wait action, then so many seconds or a minute later run the Get Battery Info and the Variable Set.
Then you can use a Say action to read the time allowed. By the way, the time is represented in Milliseconds!!
So in the Variable Set, use
Name
%BattLevel
To
%bi_time_until_charged/60000
Do Maths: yes, check that box
That will render the %BattLevel in "minutes"