I've replace the batteries in the fobs but the car doesn't respond at all. I can still drive by inserting the fob into the slot and interestingly, the car will respond to the fobs for about 24 hours after the car has been driven. Is the the system battery powered at all by a separate battery to the main one? It sounds like when the car has been used, the battery is topped up but isn't holding charge for very long. Any ideas or is it a new receiver module?

There is evidence to suggest that our cars do not respond to cheap batteries in the remote(s).

You don't state what make you installed but I would try duracell before looking any further for diagnosis.

Both fobs suddenly stopped working at the same time, I replaced with energizer batteries again and still nothing so I think it must be deeper that the fob batteries.

Can you lock/unlock the car by having the fob near and pressing the button on the door handle?

Passive or non passive entry?

Any fault codes?

State of charge of your car battery(s)?