[werk_ag]

Battery backup in the RX unit is not necessary, but does have benefits. For me, I chose to plug my RX system into my computer's UPS (Uninterruptible Power Supply) which I use to keep my computer and modem/router running during a power failure.

Thats is also my approach.
WeatherDuino and computer on the same UPS.

Router its on another UPS, because they aren't physically near.

If the RX box looses power does the TX store the data until it comes back up ? or
If the RX box has battery backup but the internet connection is lost does the RX store data until the internet works again ?
Can someone please help clarify ?

As said by Palmyweather, the TX unit only records the rain tips.
The receiver have a data logger included, exactly with the same functionalities as the Davis data logger. Whenever the receiver keeps powered, data is stored at the user defined interval (5, 15, 30 minutes). So if for any reason, the user have to switch down the computer where Cumulus (or other software) is running, then, when you  restart Cumulus, it will fetch from the logger, all the data since the last time on.

PS - got the RX box fired up yesterday and it seems to work. Not fully tested yet and still waiting for a few bits, but a good start.

Please keep us informed of the progresses, this always help other users.