I am going to be docked on the water far from an electrical source. How long is too long to run an extension cord to my batteries? (amp loss?)

Thanks,

Brandon

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There is no set in stone rule on this. It all depans on the load  (amp draw) and the distance of the line run.  I would say as a rule of thumb to us the largest gauge wire extenation cord you can buy. 12 gauge or larger I will tell you now they will be expensive. The typical orange cord you by is 16 gauge. How far is the run (feet) what is the load rating on your charge (name plate FLA / full load amps ) is it a trickle type charger or a auto car charger?

A 50 amp charger would only draw around 5 amps on the 120v Side. A 10 amp charger would only draw around 1 amp. you may not need as big, wire size, of a cord as you would think.

2 bank, 20amp

It that 20 amps total? then it will only draw approx 2 amps on the 120V side.