No input beyond gratitude for making these videos. Most channels gloss over the mundane tasks you give us a peek at and your stuff really helps give us an idea of the daily battles fought by boat owners. Also, I'm super stoked to follow along the mini loop!

Thanks. This was helpful. Looking forward to hearing about the root cause and solution to the battery charger grounding (maybe ?) issue ...

After you turned on you battery charger your hull potential quickly shifted down and then slowly rose while your batteries were charging. Your charger's ground cables are introducing a voltage drop (V=IR) that's being detected outside the boat by the Corrosion Reference Electrode. During the transit time of recharging your battery(s) your zinc anodes are experiencing accelerated corrosion (a.k.a "Electrolytic Corrosion", "Stray Current Corrosion"). However, your situation does not appear to be severe as the maximum voltage drop was only 50mV or so. Regardless, make sure your battery charger ground wires are oversized and have good electrical connections to each of the batteries being charged and that you have excellent ground connections to (and between) each engine block. Think about it -- if every underwater metal is connected together with perfect grounds (i.e., 0.00 ohms) they can only ever be at the same potential. Your hull potential would be unchanged whenever any electrical device was turned on or off. Also, don't forget to include in the testing your engine alternators at max RPM.

Pretty good system, pretty good teacher lol

as usual Capt. Tom good info thanks I use magnesium in fresh water anodes pretty used up each season I have bought my anodes from this company before. I have my battery charger on quite a bit so the shore power is usually plugged in alk in michigan

Check and see if the ground wire on the battery charger AC was accidentally put on the DC ground buss bar. And see if the DC ground was accidentally put on the AC bus bar.

Very interesting test. I've seen divers at our marina use these before they dive on boats. Never thought about picking one up until your video. I was also wondering what you had done about your anodes after moving down from NY to FL. What anodes do others use in Cape Coral? Hope all is well. Thanks for the video and making me spend more money. :) C & G.

If I followed along correctly, it seems like you tested out ok. Maybe just switching from zinc to aluminum is all you need. That's what I use on my outdrive, however it isn't permanently in the water like your boat. I also have the Volvo Penta Active Corrosion Protection system - maybe that's something to look into?

Have you thought about changing the type of zinc? Aluminum, magnesium, etc.?