Thanks for your comments V.
It was the testing of my current car battery, that Gordon was referring to rather than Tuyens battery.
I agree that with some mechanics, you would be scratching to trust them with changing an oil filter, never mind electrics
. Fortunately, the mechanic I use knows his auto electrics and has a proper battery tester. His machine has confirmed what I thought.
The (old car) battery is stuffed. It will charge up, but the 0.02 amp draw (according to my el cheapo multimeter) kills it in a couple of days, where as it used to last for ages.
I take on board your advice regarding the testing of AGM batteries.