TOPIC: Start or Deep Cycle?

I need a new battery to run my accessories :

* pair of 55 watt docking lights
* 500 gph auto bilge
* nav & anchor lights
* horn
* fish finder

I do lot of night fishing. The stern light & sonar are on most of the time (all night) and the docking bow lights can be on for extended periods of time. I'm going to add a 2nd sonar and a searchlight at some point.

It came with a deep cycle and seems like that's what you'd use but I'm not sure which is best. Do I go with start or deep cycle? The starter for my 50 horse Merc uses a separate battery .

Thanks.

Well if you have a seperate battery for starting then go with a deep cycle.Without going into great detail the deep cycle will hold more juice for your accesories over a longer time period that a starting battery.

Definitely need a deep-cycle to run the accessories Z-man. Keep the start battery for the Merc completely separate, two different systems, if you will. The alternator on the Merc can keep it's own battery charged up, but the other system should be charged with a 110v "smart charger" when you get back to the house or the dock!

Case in point;

We had a customer come in yesterday to purchase a battery isolator for his inboard boat. He was running three batteries, and having all sorts of problems. Someone told him he needed to install a battery isolator to correct the issues. (Partially right advise, but please read on.) He had already "burned up" the original alternator on the Mercruiser, and had upgraded to 100 amp (albeit still too small) model. Two of his batteries were used for extended running of elec. equipment such as yours, and were frequently run way down on charge by day & night long fishing expeditions.

The problem now is the insulation is melting off all of the battery cables from the amount of charge the alt. is trying to produce to bring the entire system back to a proper state in a short time. Alternators are designed to maintain a battery, not recharge them from nil on a regular basis. (Confirmed by Motorola/Leece Neville/Prestolite and other manufacturers).

At his insistence, we sold him the isolator anyway, but I expect his problems are not over. Sorry for the long post, I just felt compelled to share that with you. Here's the link to a good thread about boat batteries that probably would have answered your question much quicker.

www.fiberglassics.com/glassic-forums/2-main-forum/25228-whats-the-deal-with-qmarineq-batteries.html#25228

Mark, We have a sailboat with a Yanmar diesel with an alternator and a "1, Off, 2, All" battery switch. We have 1 deep cycle and 1 starting battery each. Typically what we do is start and run the motor with the battery switch set on All and when we are sailing or at anchor switch over to the deep cycle battery. The batteries are connected via battery cables that go Neg. to Neg. but I'm not so sure about the Pos. connection but I presume that there is a Direct connection there also. When you say that the 2 types of batteries should be Completely separated, do you mean to say that the way we have ours hooked up in conjunction with each other and/or the use of the battery switch is damaging our batteries? I think I may know what your answer is going to be in light of the fact that we had a brand new battery crap out after only one year and the other after only 2 years with not that much use. Thanks.
Shipster

News I can use! Thank you all for the helpful information! From everything I've read it looks like I'll be going with a deep cycle lead acid type battery for those accessories.

After a trip, I always put it on a charger/maintainer. I want to be sure this is the way to go. Maybe some of you fellows with more intimate knowledge of marine electronics can chime in here- It's a 3 stage 12DC/1.5 amp, on/off trickle type with thermal overload protection as well as short circuit and polarity protection. Here's where I might be getting into trouble with it- it cannot charge a battery with less than 9 volts on it. May I presume that I can check that with a multi-tester? If below 9 volts what do I charge it with? Also, may I set up a solar charger to use while on the water? If so, what would be the specications for that set up?

Thank you all again.

You may want to consider a trolling motor battery charger used by bass boaters to recharge their deep cycle trolling batteries. Designed for the task, many mount in the boat so you just plug them in instead of dragging the charger out after every trip. Similar to this. www.basspro.com/Bass-Pro-Shops-XPS-Intelligent-Technology-Series-OnBoard-Marine-Battery-Charger-XPS-iT-5/product/10210664/-1759705

I think I've got something like that. It's on the battery all the time, plug into the wall when you need it.

An islolator allows the batteries to be charged at the same time but does not let them be discharged together.Batteries will seek each others condition/level if wired together. So if you have a new one and a old one hooked up without a isolator the bad one will constantly drain the good one down untill there about even.The isolator will allow them to be charged but not discharged off each other. The deep cycle likes to have a long low amperage charge and the starter will take the quick charge off the alternator.A low amp automatic trickle charge is usually better for the deep cycle.
Now if you charge the deep off the alternator it will draw the full amperage and then some putting a max draw on the alt.

I have 3 chargers, one for each battery. Each battery: start, trolling and accessoroies is completley isolated from the other. So I think I'm set up pretty good. Does a '67 Merc 500 Thunderbolt have an alternator, stator, or some other means to charge the start battery?

If your motor has a tach and it is working then your alternator is working.In theory if it is idling and you disconnect the battery cable it should/may die,if not working.If reving it up and you do the same thing and it does not die then it is probably charging.I do not believe the motors of that era had a large output,I am thinking 40 amps max, may want to post in the Merc section for the gurus to give a "certified" answer.You should have a charging system on that motor.

Sounds like you're set up pretty good then Z-man, happy Boating! Here's my new charger;
www.fiberglassics.com/glassic-forums/20-product-reviews/33509-bosch-qsmartq-battery-charger.html#33509

Shipster, I know there are a lot of boats set up the way you described. They will work that way, but as Mr.88 described and you have already found out, it doesn't do much for the life expectancy of the deep-cycle battery. If it were me, I'd leave the selector on the start battery, and save the "Both" setting for emergencies. Charge the deep cycle as described above, and they'll last a lot longer!

88 and Mark, Thanks for the info. I'll be getting an isolator asap.
Shipster