NOCO Genius GENM2, 2-Bank, 8-Amp (4-Amp Per Bank) Fully-Automatic Smart Marine Charger, 12V Onboard Battery Charger and Battery Maintainer

I was a little skeptical at first, but went ahead with the purchase based on reviews. After unpacking the item, I was impressed. The enclosure is larger than I expected, but very well built and sealed. The leads are large guage wire and well-insulated. Although description states "on board" charger, the manual cautions against charging when in the vehicle without disconnecting ground lead. I did a bench test where i purposely used a bit of one battery and left the other fully charged. Then connected leads with the two negatives hooked together. As i expected, the charger separately sensed and properly maintained each battery independently.I also very much liked the fact that the charger includes an electronic relay for charge output - this means when charger is de-energized (not plugged in to AC), there is no connection to the charger circuits. For protection of both charger and alternator, do not attempt to leave the charger plugged in while vehicle is in operation -- although there are protection mechanisms built in and it is very unlikely to cause damage, it is not recommended.This charger is now installed in my truck which has a dual battery system (isolated by a solenoid). The truck sits unused most of the time, but now, i don't have to worry about having a dead battery when I need to use it. I've also found that the vehicle's charging system doesn't necessarily do a good job at managing the dual batteries; the alternator charges the two batteries as if they were one thus the primary battery tends to not be fully charged and thus slowly, over time, the primary battery has degraded performance. With this charger, now the primary and secondary batteries are independently maintained and thus both are kept at optimal performance.

First point- If you are considering buying a charger or not buying an onboard charger, stop considering and buy one- imagine a world where you never again have to wonder “hopefully the boat will start today...” by having two batteries and an onboard charger you basically eliminate ever having the possibility for a dead battery again- even if one of your batteries is dead and/or your engine charging system stops working, you have another battery you can switch to so you have plenty of charge to get home... After doing it, it seems like the most obvious investment a boat owner should make and elimates so much heartache- I will never own another boat without it. Specific to this charger, it’s simple to use and install and has worked perfect every time since I purchased it 6 months ago. I cannot say I’ve tried others to compare it to, but I can say this one feels extremely solid and is very easy to use. The only other product I purchased for this is the basic 3 way battery switch- a neighbor who is a retired electrical engineer for a boat manufacturer said the one-way protection fuse stuff they sell is unessisary and I haven’t had any issues. I use one deep cycle and one starting battery. I also would add that prior to installing this, I was occasionally having issues with the radio turning off or shutting off when the boat was off- by adding this, somehow I’ve elminated that issue alltogether.

I bought this to replace an old "World's Foremost Outfitter" store brand charger that went kaput and managed to pull my two month old deep cycle battery down to 4 volts. I was concerned the battery was toast. I shopped for a decent two bank charger that would condition batteries to help with sulfation, and landed on this one. Based on cost and reviews I went for it.The deep cycle battery was too dead for this charger to initially detect it, so I had to hook it up to a "dumb" charger for about 24 hours to get the voltage high enough for this charger to detect it and start charging. Once it detected it, I let it sit. It took about 48 hours to get from 12 volts to fully topped off and conditioned at 13v+, but it pulled it off, and the next day I took the boat out and got a full day of trolling off of that battery. Super duper satisfied. Now when I plug it in after a trip, the batteries are topped off overnight.Side note: one review mentioned a concern about the waterproof nature of this product. I was curious about that so I took the rear cover off. The inside of the unit is completely sealed with epoxy potting compound so I'm 100% confident that it is waterproof.