I actually emailed CTEK, asking them about the recommended charger for the M2C. Here's their response:
Hello,
We recommend the BMW branded charger which is manufactured by CTEK. For more information on this product please contact your local BMW dealership.
As for a CTEK branded charger, if your battery is lead-acid or AGM you have many options. Our MXS 5.0 is designed for charging and maintaining lead-acid and AGM batteries up to 160Ah. If your battery meets this criteria our MXS 5.0 will also work great.
https://smartercharger.com/collectio...s/ctek-mxs-5-0