In my car a Varta Blue Dynamic B18 with 12 V and 44 Ah is installed. I bought the car only recently used. One day the engine did not start, battery had 11.8 V. Then I charged the battery at home with a charger, shortly afterwards the voltage was 12.5 V. After a few days the voltage was 12.2 V, although the battery was only standing around. However, the measurement results can be enjoyed with care. (How can I get the accuracy of the measuring device ts check?) Then I put them back in the car and the engine started again. However, I am now afraid to drive away, because then I might not come home and then have to look for start-up help. How can I check if the battery is still ok or I need a new one? For example, would it be a measure to start the engine, to turn it off immediately, to start it again, etc. and to see how often this works, and if it is less than X times klap pt to buy a new battery? I have a multimeter, but I have no idea how I can measure flown charge, for example, to measure how much charge between “full” and “empty”, or vice versa, flows pure during the charging process. Thank you in advance for your advice!