Foxwell BT100 Pro Battery Tester

Although my D2 starts first time and is showing no signs of a weak battery, I have been getting suspicious that all may not be well. At 830 CCA it is smaller than I would like, and if I do not drive it any decent distance for a week or two I put it on an Optimate 4 trickle charger which immediately goes into the Red - Battery Recovery mode. Unlike all the other batteries I charge which go into maintenance mode after a few hours, it will still be actively charging the D2 after a couple of days. So I bought a Foxwell BT100 Pro Battery Tester and it shows 232 CCA available, a State of Health of 23% and Replace Battery in big letters. God knows how the thing starts.

All my other batteries are fine, including the one in my Triumph TR2 which I last changed in about 1992, but which pretty much stays on a trickle charger - that is showing a State of Health of 95%.

I've ordered a Tanya C31-1000 BTW.

For £36 this is a useful little gadget that gives much more info than a multimeter. I would have stuck this is a Product Review section if we had one....
https://www.ebay.co.uk/itm/FOXWELL-12V-Auto-Battery-Tester-Load-Analyzer100-1100CCA-Scanner-Tool-BT100-Pro/392491791647?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649