There is no problem with using a Planet T5 system with P94 - I have one and it works fine. I gather that yours also did until "something happened". It may be that somehow the radio has gone back to the original setting used by aircraft and helicopters, and that the neutral throttle signal now corresponds to full back stick. I always recommend fitting a spring-return to the throttle stick on these transmitters. In all events you have to switch the Tx on with the throttle lever in the centre of its throw, and leave it there until the relays have sung their song. Alternatively you may have accidentally connected up something wrong or shorted something when you were moving the batteries and blown the two little diodes between the terminal blocks. That's a ten minute fix.
When you're dealing with a dirt-basic Chinese radio designed for very-cheap-things-that-fly then you will come up against problems which otherwise wouldn't exist or could be programmed out. I suggest trying the P94 with a different Tx and Rx - preferably one of the "normal" brands such as Futaba, JR, Hitec, Sanwa, Robbe-Futaba etc. If it still misbehaves then send it back for us to examine. If it's OK with the other radio then the problem lies with the Planet radio................and good luck getting any sense out of the UK importers! Shame that they now also have the Hitec agency.