The BCRs are not batteries but capacitors that discharge over time. The downside of using them is if the engine has not had power on it after a couple of hours, you need to recharge it by waiting a minute for it to charge. Kind of a hassle if you want to switch on power and immediately start running your trains. The upside is they never go bad (supposedly).
PS1 and PS2 5 volts systems use the BCR 1 while PS2 3 volt systems use the BCR 2. Make sure you get the correct one. PS3 engines were built with a capacitor.
Most of my PS2 engines now have BCRs.
