https://www.amazon.com/BLACK-DECKER-.../dp/B0051D3MP6
Get yourself one of these. 6v and 12v float charger.
Buy a set of Delphi connectors off eBay amazon etc. and make a charging lead for the battery. Then you got one charger for both batteries assuming you have a fish finder with a lead acid battery.
Hobie charger is like 40-50$.
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