I am trying to link data from worksheet Electric 2018, using an absolute reference and dividing it by data from the a cell on the 2nd worksheet. However only the data from the 2nd worksheet stays absolute but the data from the first worksheet does not.
Neither of your range references are actually absolute. They are both mixed references. $C7 locks down column C, but allows the row reference to move. C$15 locks down row 15, but allows the column reference to move.
I think you are dragging the formula downwords. In that case your 'Electric 2018'!$C7 will change because you didn't fixed row number if you want it as absolute then you need to fixed row number as well, like this 'Electric 2018'!$C$7.
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Please explain EXACTLY what you are doing that leads to it not working the way you expect.
If I want to re-create what is happening to you on your side, I need to know the exact steps you are doing that causes this to happen (simply saying "it is not working" is not enough for us to help you!).