Please note that I am not a battery expert, but I am an aircraft maintenance technician with 32 years experience so take the following info with that in mind:
Dear All,
I am replying after much deliberation if I wanted to go down this rabbit hole or not. Here goes.
Different battery chemistries require specific charging algorithms, i.e., charge voltage, rate of charge (amperage/hour), end of charge detection, etc. While the battery might not explode or catch fire (possible like in some cell phones), it certainly will ruin the length of service and performance of your battery.
The brown and green chargers have different power supply voltages (that should be a hint?).
The fact that you can use a green power supply with egg charger must indicated that here is some voltage regulation (down) in the internal circuit. I don't have one to be able to confirm this, but suspect that it is true.
The RB has two polarity keyways in its battery compartment that allows it to use all three batteries types by design. By "manipulating" the "polarity key" on the battery case, you can use either brown, green or white batteries in the UGOBE Pleo. The Pleo will not care if the battery chemistry is Li-poly , Li-ion , NiMH, or NiCad or whatever.
This requires extreme care when placing the battery in the Pleo in correct polarity (match the pads on the battery to the springs in the base of the battery compartment).
Both the brown and green charging cradles have battery "detecting switches" in their polarity key slot. If you have used "cut the key off" technique to use a different battery than intended in your Pleo, its own charger base will not detect it now and will not charge !
What to do? Using a suitable material that will securely hold the tiny little detection switch "fully compressed" , i.e., not sticking out into the keyway hole.
Use the above information at your own risk and I didn't tell you to do it!
Peter