Start or Deep Cycle?

[zonaman]

I need a new battery to run my accessories (12v system) :

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

I'm going to add a 2nd sonar and a searchlight at some point.

It came with a deep cycle but I'm not sure that's best. Do I go with start or deep cycle? The starter battery is a separate battery for my 50 horse Merc.

Thanks.

 

[Boatist]

Re: Start or Deep Cycle?

For a starting battery you can use either a starting battery or deep cycle since motor is 50 HP. Starting batteries are cheaper and have longer warranties. Costco has 3 year free replacement and 100 month prorated warranty. Deep cycle will take a little more abuse but cost more and have shorter warranties.

If it is an older 50 hp motor then likely does not have a very large charging system. With what you listed so far the highest drain is the docking lights but assume you will not use them very long.

If you add any high drain battery loads like a large stereo or trolling motor then you need a large deep cycle for those loads and I would not try to recharge that battery with your outboard.

Starting batteries should not be discharge below 80 percent of full charge. Deep cycle can be discharged down as far as 50 percent.

What ever you buy make sure to get some type of automatic or smart battery charger. I suggest something with 10 amps or more per battery.

How long you leave your batteries discharged will have a major impact on their life.

 

[zonaman]

Re: Start or Deep Cycle?

I charge all the batteries after each trip. Right now I a use 3 stage 12DC/1.5 amp, on/off trickle type with thermal overload protection as well as short circuit and polarity protection. One on each battery. Are these adaquate? Here's where I might be getting into trouble with the accessories- it cannot charge a battery with less than 9 volts on it.

 

[KD4UPL]

Re: Start or Deep Cycle?

If you're running your batteries down to 9 volts you will need to replace them very rapidly, like after each trip. Your best bet is a starting battery to start the engine and a deep cycle for the accessories. Use a voltage sensing relay to charge them together when the engine is running and isolate them when it is not. 2 dual purpose batteries would also work well for you as none of your loads appear that large.

 

[zonaman]

Re: Start or Deep Cycle?

If you're running your batteries down to 9 volts you will need to replace them very rapidly, like after each trip. Your best bet is a starting battery to start the engine and a deep cycle for the accessories. Use a voltage sensing relay to charge them together when the engine is running and isolate them when it is not. 2 dual purpose batteries would also work well for you as none of your loads appear that large.

Don't know if I am- The trolling motor is a Minn Kota with the 5 light indicator and it never goes down past the the 3rd light, The starter never is a problem either. I use those docking lights for about 10 minutes or so at a time on the accessories battery with the nav lights and sonar going too (all accessories are fused).No trouble till last trip. I don't have voltmeters on any of those. The accessories battery shows 10.98 on the multi-meter, it gets the nav lights on but they flutter and go dim. The dock lights (which are wired through a relay) won't go. That battery (a Walmart deep cycle) will not take a charge. I'll have to have it load tested.