The last time I rented a car (2 months ago?) if you returned it less than whatever you receive it at, you get charged for an entire tank of gas with the $3-4/gal markup. So receive it full and return it at 15/16ths and you're looking at a $80-100 bill easily on the larger vehicles.
It's likely similar where if you receive it at 100% and return it at 98% you're getting charged the full $25. It's just another revenue source for the company.
The refill charge is nuts anyway even for ICE vehicles. Put an 1 m³ construction site tank+pump for diesel and one for regular gas on the site and that's it - these things cost about 1000€ [1].
From the start, refill charges have been an utter scam.
It's likely similar where if you receive it at 100% and return it at 98% you're getting charged the full $25. It's just another revenue source for the company.