This is a genuine BMW heat insulation battery, part number 61 21 8 366 155. The number stamped on the part is 61218366155; BMW's catalog files it under the short number 8366155. You will find it on our Electrical shelf, under Battery with holder.
It fits the E36 sedan, coupe, touring and compact (318i and 318ti, 1992–1999), with the M40, M42, M43 or M44 engines — and the European-market versions.
BMW draws it on 2 diagrams, among them Battery (61_0065) and Battery, empty (61_0141). It weighs about 176 g (0.4 lb).
We have not had one on the shelf yet. Request it and we will tell you when one comes off a car.