running on empty

be running on empty (to continue perfoming or functioning even though you have little energy or strength) — продолжать что-л., когда сил уже не осталось или силы на исходе; держаться из последних сил; продолжать, хотя непонятно, в чем душа держится (и как ноги носят)

Example 1: With all the demands from a full-time job and college, Lori has been running on empty for the past couple of months. I don't know how much longer she can continue this way.

Example 2: Have you ever felt as though you were running on empty? I sure have, and I’ll bet I’m not the only one who could make that confession.

cf
[на последнем издыхании]
[еле дышит]
on one's last legs
[run out of steam]
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“Running on empty” is an automotive idiom. It’s used to describe the experience of having no fuel, but pushing on anyway.

The person running on empty appears to have no reserves of energy to be able to continue what they are doing. There is also the sense of surprise and wonder that they can do this. It's like the car engine that keeps running despite the fuel gauge showing 'empty'.