RV3028 VBatt Resistor Value

I was looking at the RV3028 RTC board from Pimoroni and I noticed that the battery is tied to VBackup via a 470k resistor.

I was wondering why the value is so high? The datasheet suggests a value of 100-1000R. I guess it limits the current to a few uA which is still a few order of magnitude higher than the 45nA required by the RV3028. But why 470K? Just a large arbitrary value?

I’ve just been looking at this - I have a new 1.55V cell but that 470K resistor is dropping about 0.5V suggesting the device is drawing 1uA not 45nA (specified at 3V). I wonder if the current rises at lower Vbat? Anyway, it doesn’t seem like a good idea to drop so much power across a resistor. Why is it there? ESD?

Oops! I have been fooled by the input impedance of my DVM. Yes my DVM was drawing 1uA, not the RV3028. I’m still puzzled by the 470k resistor though. Wouldn’t the useful battery life be longer without it?