This is the 11757th most frequent German word.
tankern
"Tankern" is not a standard German word, but it may refer colloquially to refueling or filling up with fuel.
The word 'tankern' here is used to mean refueling a vehicle.
Ich tankere mein Auto voller Benzin.
I refuel my car with gasoline.
In this sentence, 'tankern' metaphorically refers to gathering energy.
Wir tankerten Energie vor dem anstrengenden Tag.
We gathered energy before the strenuous day.
This is a figurative usage of 'tankern' to indicate building up courage.