batteries?

[boatman37]

so this winter i want to replace my starting battery. i have been having an issue recently. boat is a 1986 sundancer 250. i use a used automotive battery for my starting/running battery. it is a duralast 78-DL 700 CCA with 875 cranking amps at 32* and reserve capacity of 120. when i bought the boat last year i bought a new duralast marine battery. it is a 29DP-DL 675 CCA with 106 amp hours and 840 cranking amps at 32* with 210 reserve capacity. i don't know much about what these mean in terms of boating...lol

so my issue is i start up and head out on my auto battery. drop anchor and switch to the house (marine) battery. the only thing running is usually the VHF and the fridge. after a couple of hours if i forget to switch batteries back i start up on my marine battery and head off then after about 2 minutes the engine loses power and shuts down. i switch back to the automotive (starting) battery and it fires right back up.

what this tells me is that my alternator is likely not putting out enough juice? my gauge reads about 12 volts but with the blower on it drops to about 11. i'm not sure how accurate my gauge is.

so after all that...

i plan to replace the alternator and the automotive battery (came with boat, unknown age) and adding an onboard charger. i currently use an autozone smart (http://www.autozone.com/test-scan-a...nic-battery-charger/523687_0_0/?checkfit=true) when on shorepower.

so my question is what battery should i look for? is my marine battery sufficient for a few hours anchored? possibly overnighting but not likely. what should i look for in a starter battery? or should i make my marine battery my starter battery and buy a deeper cycle house battery? or am i overthinking this whole thing and just buy a new battery? lol. i bought the boat from the original owner and he said the alternator is the original so 30 years and about 600 hours. i plan to replace it regardless of its output as i think that is the root of my problem. but it only seems to be an issue when i forget to switch back to the starting

thanks and sorry for the long post but wanted to try to add as much info as i could

 

[ondarvr]

It should read around 14+ volts when the motor is running, deep cycle for house, starting for starting, marine in both types.

 

[alldodge]

+1 agree and will add

Your killing your house battery with it running down enough to kill the motor. You need an ACR or at least an isolator, with either the battery switch is not needed and the alternator will keep all of them changed.

 

[boatman37]

i do have an isolator.

i am surprised that i am draining the house battery that quick. the longest i am out is maybe 3 hours and only the VHF and fridge running. i would turn the fridge off but it automatically switches from AC to DC and i know i will forget to turn it back on when we get back in...lol. i don't think there is a way to turn it off when running on DC only.
to add, it will start back up on the house battery so if my alternator were putting out enough juice then i would think it would be fine. if it is that low that it dies after 2 minutes then i would doubt it would have enough juice to even start it up?

 

[alldodge]

Have to agree with your thoughts, but then again how does the engine die due to lack of juice if the ALT is putting out 14V and the isolator is working? Maybe the isolator diode has opened up

 

[boatman37]

possible on the isolator but as far as your first question i don't think the alt is putting out 14v. if my gauge is accurate then i am only putting out 12v or so. and it does seem like it is a little lower reading than it was at the beginning of the year so it may be on its way out.i always run my blower at no wake speeds and it reads about 10.5 or 11 with the blower running. i need to test it with a voltmeter while running. going to try to spend friday working on it and a few other things

 

[JoLin]

i do have an isolator.

Check it again. If you have a battery switch, you may not have an isolator of the type alldodge is talking about. Every boat that has shore power needs to have a GALVANIC isolator installed in each AC circuit. It's a 'box' similar in appearance to a battery isolator, but it performs a different function.

My .02

 

[boatman37]

not sure JoLin. i know i noticed it and asked the original owner and he said it had an isolator. it is mounted to the transom and finned. i will have to get a pic of it this weekend. my battery switch has off-1-both-2. (2 battery setup).

 

[JoLin]

Gotcha. My boat has 2 galvanic isolators (one for each AC circuit), the same type of battery switch,,, but no battery isolator or ACR. You'll have to get whatever info you can off the unit that's in the boat. If you google the 2 types of isolators (galvanic vs battery), most look very similar, right down to the finned housing.

 

[Keith Ogden]

No Title

I killed my Auto zone smart charger in one season, melted out the board.
I switched to "Next Generation Pro Sport 20 Part # 42028" for shore side charging.
I also use a "Battery Doc? 12 Volt 150 Amp Battery Isolator" for on board charging .
Has worked out well . Charger never gets hot. and I like that it automatically reconditions the battery's .
The Battery Doc works as it should , cycles between battery's as it needs to to charge while on the water.
There is a light on that shows what battery is being charged while under way.
Only thing I had to do was add a switch so that I can by pass it while on shore charge ,
as the Doc will still try to switch between battery's if used with a shore charger. And the shore charger will do it instead of the Doc.