I would also be interested to know if it contains an active battery management device to control the charge & balance of the cells when used with a bike charging system designed to work with a lead-acid battery.
I have never yet found an MZ replacement battery rated at the OEM 12AH. However, various manufacturer's widely available same physical dimensions 11Ah versions have worked fine for me for the last 31 years on my TS250/1. Google 6N11A-3A or -1B (the difference is the terminal layout).
For preference I would buy a Sonnenschein brand, but I think they have stopped making them. Next would be a Varta or Bosch (both made by Johnson Controls - probably the same battery marked differently).
Currently using a Saito brand (probably Chinese or Taiwanese) bought from a Louis store in Germany. Only downside to buying from a German retailer is the need to bring back an old battery for recycling or you get charged a deposit that gets refunded when you bring the dead one back. I did this in person while over there in the motorhome one year & remembered to take a dead battery with me.
MZs need a halfway decent battery to run the bike at low revs, as the dynamo doesn't start charging until the revs rise well above tickover. At 60W continuous rating, the dyanmo is a bit marginal - sitting at a traffic light at tickover with the headlight on (45W + 5W + (4x2W)), indicators on (42W + 2W intermittently) & holding the bike with the rear brake (21W brake light on) plus the ignition (10W ?) will all be being supplied by the battery. On short journeys in heavy traffic, the battery may not get fully charged, requiring top-ups from a charged when parked.
An electronic regulator will help get the best from the dynamo, but best (and priciest) option is a Vape alternator kit - 180W rated 12v complete replacement unit with built-in CDI ignition.