Yes it is - gives you a longer memory retention with the power off.....
A-B have a history of not using rechargeable batteries, probably wanting customers to buy their backup batteries... all that has changed with the L7x series of processors... see below.
A short summary.....
L1 and L55 processors use battery power to retain the memory while the power is off. The longer the power is off, the more battery power is used, so don't keep the processor powered-off for long periods.
L6x series processors use battery power to transfer the volatile memory to flash memory each time the power is lost. The more frequently the power goes off, the more battery power is used, so don't keep switching it off repeatedly.
L7x series processors use an "Energy Storage Module" which is charged while under power, and is used to transfer the volatile memory to flash memory each time power is lost.