DIY BMS or do it yourself battery management system.
I really want to move to Lithium iron phosphate batteries onboard (not gonna explain the pros and cons) and drop-in solutions are overpriced and do have issues anyway. Also it needs a lot of different controll compared to lead acid batteries. So just not to be too bored with volunteered isolation while moving between countries I found out about DIY BMS (You can find a lot of details on youtube and while googling). People are using it mainly for powerwalls but I thought why not to give a try for a boat as well? DIY BMS

Just for a proof of concept it was easier to use Lithium-ion batteries to get a 12V bank. DIY system can have cut-in/off relays as well when voltage or temperature is too high or low. DIY BMS Relay

As it can send data to InfluxDB and as I have Raspberry PI onboard as main computer anyway I decided to connect it together via WIFI. Raspberry PI

Another challenge was to install something like ammeter. As I was completely new at Arduino world, I made some mistakes and bought not the most suited chips, and had some try and fail days when connecting resistors and capacitors and reprogramming (can I say firmware? :)
So here it is - Arduino Nano sending Amps from ADS1115 through EPS8266 wifi chip to Raspberry PI. DIY Ammeter

All can be seen in Grafana dashboard which is read from InfluxDB.
So here it is - Arduino Nano sending Amps from ADS1115 through EPS8266 chip to Raspberry PI. DY BMS Grafana

And there you see the result - tiny 12V 12Ah battery bank! (each cell is 6000mAh). It still needs proper wiring and fusing and a voltmeter for total bank voltage. Also I really want to install MPU9250 gyro sensor to send more data to the autopilot onboard. But it seems that Sail Map app needs more of my attention for now. DY BMS Grafana