(enhancement) Electric charge readout.

[NightOps007]

Add charge readout for machines(especially accumulators) and equipment grids(cars/tanks/locomotives) that show percentage(0-100).
An example of how this would be useful is when using electricity from grid to power trains(zelectricvehicles mod) in conjunction with something from the grid charging the battery equipment in said train, like inductive charging coils. Don't want my trains leaving until the batteries are full.

[0ptera]

Accumulators can be hooked to circuit network in base.

Reading from stationary vehicle grids is of limited use.
In your example the charging coils should provide a signal if charging is done, as that Mod already has made a connection to the battery modules.

It can also be done by monitoring the grid power through an accumulator https://forums.factorio.com/viewtopic.php?f=8&t=23130

[NightOps007]

Tesla coil has no circuit connection.