Question about Garmin Striker Vivid 7sv

Any type of battery with at least 12V
Personally, I use a 17V lipo 5s battery.

I use a lithium battery "TMCT 12V18Ah Lithium Pro", with max. current consumption of 1.5A you can fish for 12h (18Ah / 1.5A).
I got it here: https://www.echolotzentrum.de/produkt-ka....
The shop is very competent and also offers so-called bundles suitable for the Vivid7sv.
Above all, they deliver the batteries by post to Switzerland - not a matter of course because lithium batteries are considered hazardous.

Thanks but my boat has no battery (rowing boat)

It is connected to the boat's 12v battery.