50g Backup Battery

[franz.b]

I don't understand. I have several 50g units but every time one of them runs out of batteries the risk of total memory loss during battery change is very high, about 1 time out of 2. If the batteries are low enough to not allow the calculator to be turned on then it is almost certain that the memory will be lost, even if the battery is discharged for only a few days. I wonder what purpose this backup battery has if it cannot withstand even a short interruption of power. I think it might be safer to change the batteries while powering the calculator with a USB cable.
I use LSD rechargeable batteries such as Eneloop and other brands.

Thanks