On the subject of car gadget gizmos I’ve been using a CTEK CTX Battery Sense Car Battery monitor for just under 1 Year now.
Available from Amazon here
this little gizmo attaches to the car battery and sends voltage and temperature information on the battery health via Bluetooth to a smart phone. The temperature is of the engine bay, not the battery. It just so happens on the 1 September 2018, I changed the battery in my car to a new Silver Bosch support mega battery with a 5 year guarantee. So I was interested in it’s health.
It stores all the graphs on your smartphone, this was the first time the battery was connected from new, so only had 60% charge, and gradually charged to 100% over a few days, when driving the car.