The Invader requires two "married" batteries - meaning a pair of batteries used together exclusively, so they start their life at the same level and die out at the same level. They must always be used together and never using just one in another device, etc.
The same principle applies to the three batteries in the RX200s. Those three batteries need to be married.
If you use two of the three from your RX, you will no longer have a married trio for the RX