En 
SvWhat does a battery isolator diode look like?
How to identify different types of battery isolator diodes
The images below show several examples of battery isolator diodes, making it easier for you to identify whether you have one in your own electrical system.
Note that in most cases, battery isolator diodes have a built‑in voltage drop of about 0.7 V. This is something you absolutely do NOT want in the charging circuit, as voltage drop is critical to whether your batteries have enough time to receive any meaningful charge while the engine is running.
This is a separating diode of the ELJA model. You can recognise this type of separating diode by the fact that it has cooling fins.
This is a separation diode of the TRANSPO model. This separating diode also has cooling fins.
This is a divider diode of the Paris-Rhone brand and is mounted directly on the generator.
It is a bit tricky as it looks like an integrated part of the generator.
But you can see that it is a separating diode by the fact that it has two B+ pieces.
This picture is of an S.E.V Marchal generator, where you can see its regulator on the left of the picture.
The actual separating diode is the red plate that is mounted directly on the generator.
This is also recognisable by the fact that it has two B+.