Charging car battery, just how?

Hello dear screwdriver I know it’s Christmas, but I’m really rather perplexed and therefore very grateful for every tip. My Punto 188 has been coughing for a few days in the morning and the clock from the onboard computer is at 0:00. So I thought about the battery (also because I drive a little, just about 2,000km a year). Since this was changed a year ago, it would have to be a bit unloaded. So I measured the battery: 12.35V. It’s a banner (with the Taurus on top), 12V and 400Ah. According to a scale at Wikipedia the battery would have to be about 60% charged. Today I then removed it and hung it to a factory new (!) charger (Einhell BT-BC 10E, 12V, 10A). On the device, however, it shows no charging current. What did I do wrong? Thought first on the charger and therefore got a new one that works guaranteed. However, without success 🙁 Thank you already now and nice Christmas evening qfix