Hi Kilo95, thanks for posting this here.
Bear with me please, I will put together a SonarMote kit that has everything that's needed (including Moteino of your choise via product options), but not the battery which you will have to source elsewhere, any LiPo will work but 1000mAh+ is recommended. I have 6 SonarMotes PCBs assembled, and need to lasercut the cases still, then make the kits.
The code for SonarMote is
posted here.
This allows very low power operation that will last a long time, and when the battery is low, the
Gateway UI will show you that and you can recharge quickly like a phone, via USB cable, then put it back in the sump well.
I should be able to prepare the kit tomorrow, unless something critical comes up.