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Why not go for a sensebender? https://www.itead.cc/mysensors-micro.html

I have one in each room, measuring temp and humidity. It works great

@ncollins That is a nice board indeed. I haven't checked because I will order some things after dinner. For me it is a must to keep the arduino Nano footprint. So I can replace the nano and nrf in some of the projects I already built.

@martim Just search for RF Nano on Aliexpress. Haven't looked for the cheapest one, just the first that says LRF24L01+. Although not certain if it is really a + version of the NRF24L01.

This is one on Aliexpress

Nano V3.0 CH340 RF-Nano Micro USB Board ATmega328P QFN32 5V 16M Integrate NRF24l01+2.4G Wireless For Arduino

$7.48

@3more Looks like you email address was not marked as verified, I unblock it manually so you should be good to go now. Keep on eye on the spam folder in case something came or will go in there. Thanks!

That looks really amazing. And I can see you all having a bbq over there

@3more thanks for letting me know, let me double check it and I'll let you know

Thank you again. I posted this question to my supplier. But also ordered some low power switching FETs. I'll solder one to the charging indicator. And hook it up to an Arduino to detect whether it has been charging. If it works as I hope. I can make some emergency lamps for when the electricity goes down.

I'll post the outcome on the forum, just in case some one else is interested.

@mfalkvidd Thank you for the fast response. I guess I have to go back to the drawing table to come up with a different solution. It also makes sense. The arduino has to be awake to see if the message that the radio detects is targeted for the node. In my case it would wake up many times by messages send to the other nodes.

Do you happen to now if these cheap chargers can work as some kind of UPS (Uninterruptable Power SUpply).

So in other words if I connect a USB cable to it all of the time and remove it when I want to take the lamp outside. Would that affect the lifetime of the LiPo battery? I have no idea how these things work to be honest. But I hope it would work like this. When a cable as attached it charges the LiPo but the arduino is always powered from the cable. When the LiPo is full it stops charging but keeps powering the arduino from the cable.