Sir Roger, No I had no problem , old battery out new battery in, the plug is a bit fiddly, needle nose pliers needed rather than my banana fingers. No programming needed.
Here are the instructions I got from Sargent about reprogramming the fobs.
Learn the key fobs - locate and press the learn button
Referring to the diagram below, locate the learn button on the circuit board inside the alarm case.
Press and release the button.
A blue LED will illuminate next to the button to indicate learn mode, which will stay enabled for 20 sec.
Holding the new key fob about 1 metre away from the alarm system, press and hold the Arm / Disarm
button until the blue LED starts flashing.
Release the key fob button, the blue LED will start flashing faster to indicate a successful learn, and
then extinguish.
The procedure is now complete.
Repeat the process for any additional fobs.
LEARN
BUTTON View looking into the
top of the alarm
system showing the
circuit board
Reassemble the alarm case
Place the battery back on top of the alarm chassis in the same position as before removal.
Slide the alarm lid over the chassis,
Hutch
https://www.practicalcaravan.com/forum/technical/54143-sargent-310-alarm