My new SunAirPlus2 is replacing a SunControl board that lasted for about 18 months and did a really good job charging my 20000mAh battery from a 12W (6Wx2) solar panel. Swapping the new board in I noticed that the charging current was nowhere near what the old SunControl delivered (1A at peak with a nice beefy Zener for protection, and with a quad control board to switch the individual solar panels off if too much sun pressure was had).
The SunAirPlus2 only ever reported about 60 mA charging current. I was hoping that it's just misreporting but it really doesn't seem to charge the battery at all. Did you add a current limiter to the circuitry, is the new charging algorithm to blame, or is that board a dud?
I **think** that is it is the Zener diode that is doing this to SunAirPlus2. They have different charging units. SunAirPlus2 likes a higher charging voltage and is more robust to higher voltages (6V in specific).
Try removing the Zener diode and see if that is your problem.