Weather station at far end of back garden (battery operated), reports
wirelessly to its display in the house. Data then goes via USB to a
RaspberyPi, which runs weather data collection and provides an HTML
webpage, which can be accessed with the Rpi acting as the server,
running on a wallwart.

outdoor (wireless) indoor display (USB) Rpi (5GHz) wifi router

Rpi connects to the main router via 5Ghz port, which has all worked
fine, apart from when the weather stations batteries die - then the
webpages on the pi have still been available, but with no updated data.

As happened mid summer for the second time - obviously cheap batteries,
because they normally last 18 months.

For the past few weeks, I have been regularly been unable to view the
webpage, to get it back I have had to reboot the pi - after which I
would regain access for an hour or so. I had it in mind that there
might be an issue with the 5Ghz wifi link. Looking at the pi, its
activity LED has continued to flash, even though there is no actual
contact.

A few days ago the display for the weather station stopped updating
data from the outdoor sensors, so obviously the batteries were dead yet
again. Very wet and boggy out there, so I left it until today.

I fitted new batteries this morning and the 5Ghz connection to the pi
has been rock solid ever since. Why would the weather station's outdoor
unit's batteries dieing, cause the pi's 5Ghz wifi to come to a stop?