Thank you for all your replies and advice, have ordered the mains adapter and will try that. Readings today are 138/82 and lunchtime 130/85...
I’m inclined to think that maybe last night on a full tummy and with heating on it could have made it fluctuate, as I find that I’m usually more aware of my heart beat too when in that situation.....so maybe it also affected the readings. Nice and steady today and that was after a morning gardening!😊