BCR is a brand name for a supercapacitor which replaces the battery in PS1 & PS2. It is a third-party product. It is available in two versions: one to replace a 9-volt (actually 8.2-volt batteries in older MTH) and the other to replace the 3 volt (actually 2.4-volt) in later PS2 locos. The 9-volt model has supercaps in series with Zener diodes to keep them even; it is patented.
It is not a battery, but has the capability of storing enough electrical power to keep the electronics (NOT the motor) operating as necessary for a proper shutdown or to precluse reversing upon a very momentary current break.
