TEAR DOWN - Diode really needed for solar charger?

[NuLED]

I had a AA charger that was getting rusty inside, so I decided to try and salvage the solar panel itself (I did).

But anyway, before I cut the wires, etc. I noticed that the circuit has a diode.

Is it really necessary?

I checked the polarity of the panel (using DMM) and the + goes to the + of the parallel AA battery case, and the - of the solar panel goes to the - of the battery connectors.

Does polarity on solar panels change? Or is it to block the batteries themselves from discharging against the solar panel when the voltage drops from sunlight?

PS - how do we tell the basic specs of the diode? It says 3, and then 817 on the diode. Web pages I searched seemed to refer to a color scheme like resistors but that's not what I see on this diode.

 

[donkey]

I have no hands on with solar yet, but my research into is getting extensive.
the diode seems to be so when the battery is charged it does not discharge onto the panels.
the diode specs I leave to others on the forum but I hope I have helped in some way

 

[john monks]

Solar cells voltage polarity is in the forward bias condition when placed in the sun. So as donkey says the battery will discharge without the diode.

 

[NuLED]

ok thanks guys