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Vbat with diode to VDD.

Question asked by Werner Meier on Nov 30, 2012
Latest reply on Nov 30, 2012 by Jack Peacock
AN2586 says:
Battery backup
To retain the content of the Backup registers when VDD is turned off, the VBAT pin can be
connected to an optional standby voltage supplied by a battery or another source.
The VBAT pin also powers the RTC unit, allowing the RTC to operate even when the main
digital supply (VDD) is turned off. The switch to the VBAT supply is controlled by the power
down reset (PDR) circuitry embedded in the Reset block.
If no external battery is used in the application, it is highly recommended to connect VBAT
externally to VDD.

I made tests with a 1N4448 Diode connected to Vbat, so that an optional Battery can be used for certain applications. Are there any concerns about using a Diode instead a direct connect to VDD?