How do repair droids repair?
 

I decided to give an all droid army a go: 1 stack of guard droids and 2 stacks of repair droids. I was promised unlimited repairs, the machine equivalent of both heal and resurrection.
The guard droids and one stack of repair droids got hit and both lost some members. I clicked on the icon "repair" and a window pops up: "there's no target for this ability".

What am I missing?

The healing ability has the range of 1, so you must move your repair droid next to the target first.

Also never let a droid stack to be completely destroyed. They don't leave a pile wreckage to be repaired.

Thank you for your swift reply.

A range of 1, just like the paladin. Why didn't I think of that?