Onboard charger .....Charge as you run

I am thinking about buying an on board charger that charges off the alternator ...I will be charging cranker and 2 batteries for 12 volt system in parallel ....Any one you fellers run a system like this if so Could i get some in put before I invest........Thanks..................................JIGGY

Don't have one, but am considering for my boat too, as it my Captain friend in NY. IMO, they're not all that expensive either. $100-$170, depending on model.

https://www.minnkotamotors.com/products/battery_chargers/dc_alternator.aspx

I think those things have been talked about a lot over on Bass Boat Central.

You might go dig around in their archives.

I have the "phase charger" from bass pro. Works great. Connects to the cranking battery and maintains charge at 13.2 any charge above is diverted to the other battery. It works great with my 04 Yamaha 4-stroke 25 horse. Very easy to use.
I used it on a 7 day fishing and camping trip and never had to change batteries. The trolling motor was used alot and the trip back to camp was always long enough to recharge the battery enough. The greatest thing about it is it doesn't wire the batteries in parallel because it used a one way diode, so I never have to worry about the cranking battery dying and not starting the outboard. (those 4-strokes are no fun to pull start)

https://www.basspro.com/webapp/wcs/stores/servlet/Product_10151_-1_10001_27369____SearchResults

Thanks brotha man...I was looking at one those ....I thinkin thats the way I gonna go.....................JIGGY
Ya I read a lot about them on BBC but I trust you guys opinions a lot......................JIGGY

Simple and sweet ....

I'm making a battery isolator for my boat (Just because I can and already have the diodes and heatsink), adding a voltage sensing circuit and relay would be a nice addition. I think I would like to add a manual overrride, a constant 4 or 5 amps to a already fully charged deep cycle battery isn't the best thing for the lifespan of the battery. Cranking batteries (And automotive) are designed to take that but they can't be cycled deeply. Like most things it's a trade-off

A well charged trolling motor battery sure did save my butt last summer when the reedblock cracked in my '76 20 HP Merc tiller, pull start about a mile from the boat ramp and half of that upstream against the current .... Luckily I had just bought a new battery a month earlier because that was a long slow trip home .... I think I'm going to like having an electric start setup that can charge my batteries this year ....

I got to thinking about how this circuit works and since the relay switches the batteries in parallel, the cranking battery may still be able to absorb some of the overcharge to the deep cycle battery plus you are going to have about a 1 V drop across high power stud mount rectifier diodes (As opposed to .6-.7V for a standard diode) that are used to isolate the batteries from each other during discharge (motor off). Between the voltage drop and having the cranking battery in parallel you may not even be able to get a 100% charge on the trolling motor battery, close but a wee bit shy which is OK as long as you fully charge on AC power when the boat is out of the water. Really that's good because it should help keep you from overcharging the deep cycle battery with the outboard charging circuit

That's a well thought out design and without the overkill of most battery isolators (you don't need anything close to the standard 70-75 amp capacity for an outboard motor charging circuit) which are made for RV's and large boats with inboard motors and high output alternators.