Hi.Guzzi, No, I didn't bother last night, so I have taken it off charge, and later this afternoon I will, take a reading, run the pump for maybe 10 minutes on the battery, take a voltage reading, then leave it for 1/2 an hour and take another reading.
Prof,
I am pretty sure the battery is time ex. Its over 5 years old and has had a hard life over the years, when my local Garage reopens I will take it there and get a proper check done.
I do not know nor am I disputing the condition of your battery, only the suggestion the stall/starting current of a typical tyre inflator would have a significant impact on the terminal voltage. Extended running might.