Here is my method of connecting 4th cell. I have obtained an undrilled cell holder from APD and drilled four cell positions staggering alternate cells vertically to fit them in. The lid has been drilled and a Fischer connecter fitted . The VR3 is connected by using a cable with a Fischer connector on each end. I did this to primarily eliminate the cell holder tee piece which has proved troublesome ( leaky !). An added bonus is that the VR3 now seems to track more consistently with the handsets

Regards

Dave Pelly