will these work on my 20 amp brushless esc and my 2 cell 800 mah lipo? its the connector on my thunderpower charger.

somehow I doubt that a jst connector would be happy with 20A running through it. If you were only gonna be pulling like 10A I would think it would be ok, but you might not be able to get as much juice through there as youd like.

If it were me, Id upgrade everything to the Deans Ultra connectors all around.

I have to agree with that. Standardization is a good thing. That way you can use the battery on different applications if you wish to do so.

I have a pair of 2100 mah and one 1650 mah, and they have Deans Ultra. I swap them out on a regular basis.

CGr.