as per our friend, you have an Interstate Battery in your car. This is the battery I removed some time ago and put it on my charger: it did not hold charge! Just barely into the green, enough for 3 or 4 cranks. The Battery is no good.
As to the glow plugs, change all four of them, remember, if one is bad, nothing will turn
Also, the idea of checking the fuse for the glow plug relay is excellent
Buy a MB battery

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"Schwarzbraun ist die Haselnuss":

1979 300D 234.000 Miles "Brownie"
daily driver,
1979 6.9 Sundays to the Tavern
and car shows "Big Brownie"