Low battery reading
 

My depth finder continuously reads low batteries even though when batteries are checked while the boat is running the batteries are fine the alternators are brand new the batteries are brand new the charger on the boat is a brand new 60 amp charger can someone tell me what the problem could be that we keep giving me a low battery indication

Most likely corrosion or the depth finder has an issue
Find where the depth finder is connected to power and measure the voltage level. If its low then trace backwards toward the battery and find the bad connection. If voltage is good then its the depth finder

Thx Dodge