Battered and confused about batteries

[bjsmelton]

I have a 1972 16ft wide body Ouchita Jon Boat that I am rigging as a bass fishing boat. I have seen a lot of differing opinions about battery setups on these forums. Some were a few years old and I thought might be outdated. Others seemed to me to depend on the boat and the owner's preferences.<br /><br />So, please offer me your opinions on battery setup for my boat. I currently have a deep cycle battery for my troller. I'm temporarilly using it to also start my 20hp Tohatsu outboard. (Side question: Am I damaging the deep cycle battery or anything else by using it to start the engine?)<br /><br />I have also purchased a starting battery but haven't installed it yet because I'm contemplating returning it for a combination starting/deep cycle battery. A salesman informed me that it would be a great backup battery for the trolling motor. He also said a starting battery couldn't run the accessories for very long. I also thought it would be better than a pure starting battery for running navigation lights, depth finder, and any other accessories.<br /><br />My marine service mechanic said the other guy doesn't know what he's talking about and he's just trying to sell me more battery than I need. He says all new bass boats, and the one's he riggs, come with a deep cycle purely for trolling and a starting battery for starting and running all the lights and other accessories.<br /><br />Between these two recommendations and all the others I've seen on the forums I feel hopelessly confused.<br /><br />I think what I'd like is to run the starter, lights, depth finder, and any other accessories with one battery and the troller all by itself on a deep cycle. That way my alternator would keep my battery charged for the lights and accessories. In a perfect world I'd like to do it all with one battery. However, here in the real world I like the idea of having two separate batteries that could back each other up.<br /><br />So...<br /><br />1) Should I keep my starting battery or trade it for a combo?<br /><br />2) Should I run my accessories with the trolling battery or with the starting or combo battery?<br /><br />3) Am I damaging anything by temporarilly starting my motor with the same deep cycle battery that I use for trolling?<br /><br />4) Would I be better off with two combo batteries so they could back each other up or is it OK for a starter to backup a combo and vice versa without serious consequences?<br /><br />5) Does any of this really matter or is it all a scam to keep us confused so we keep buying more and more batteries we really don't need?

 

[Ralph 123]

Re: Battered and confused about batteries

IMHO, your mechanic is correct. You want a deep cycle battery as the "house" battery. Deep Cycles are made to withstand being deeply discharged w/o damage. Regular batteries, like starting batteries and auto batteries are not. When they repeatedly discharged below a certain level they become permanently damaged and will never again hold a full rated charge. Deep cycles are made with really thick plates inside the battery to withstand the repeated deep discharge/charge cycles.<br /><br />Starting batteries are designed to supply lots of current (75-400 amps typ) for 5-15 seconds. While visually and chemically similar to deep cycle batteries they are made differently. They have a greater number of thin plates compared to deep cycles, providing more area for the chemistry to take place.<br /><br />A dual purpose is built more like a deep cycle it compromises plate thickness and adds more of them to give you the high burst of current needed for starting. Duals may be appropriate if your engine is running frequently and your non-running electrical needs are small.<br /><br />I would buy a starter battery purely for starting and a deep cycle for eveything else. I would wire them together with a combiner like the West Marine Combiner 150. It allows them to share the charge and automatically isolates them during discharge. You don't want to have to remember to parrallel the batteries to charge the house when you are underway. Better to make it fool proof. <br /><br />This way, you can always get home (the #1 goal is to NOT be stranded due to a dead battery - safety 1st, 2nd and 3rd)<br /><br />Just for the record, I am an Electrical Engineer. I studies these issues because I decided to strip my 1979 twin Formula down to the hull and rebuild her from scratch. I was therefore forced to rewire the entire boat from scratch myself. I designed and installed the wiring 100% myself. I figured if I was going to go through all this I wanted it to be as close to ideal as possible.

 

[Paul Moir]

Re: Battered and confused about batteries

If being stranded is any concern then I agree with Mr. Spencer, two is better than one. For the deep cycle, I would consider getting an AGM (absorbed glass mat) battery. They naturally have a very low internal resistance, making them also useful as a starting battery for emergencies. If I didn't care about dead batteries, and I did care about weight, I would just have an AGM deep cycle battery on board.<br />They also have the useful feature of having all the electrolyte saturated in the mat, so if you drop one you don't have a puddle of acid.<br />Personally, I have a smaller outboard (28hp) which I use a surplus AGM telco backup battery to start. I've also used it for checking starters on various other engines, including a monster solenoid/starter from a westerbeke deisel.<br /> Product Literature<br /> Useful FAQ

 

[bjsmelton]

Re: Battered and confused about batteries

Ralph & Paul,<br /><br />Thanks for the info. I'm definitely going with two batteries but I'm not yet sure what kind I want for the motor and whether I should connect my lights and other accessories to the motor battery or the trolling battery.<br /><br />One thing I found very interesting at the http://www.windsun.com/Batteries/Battery_FAQ.htm#AGM, or Absorbed Glass Mat Batteries link that Paul posted is the section titled, "Using a deep cycle battery as a starting battery".<br /><br />This section mentions that there is generally no problem with using a deep cycle to start an engine. It also implies that since many autos, boats, & RV's are laden with "power sucking appliances" (stereos, depth finders, lights, etc.) that a deep cycle battery is more suited to these situations.<br /><br />Since I'm running a small 25hp Tohatsu and my trolling battery is rated for 405 cold cranking amps in addition to the 75 Ah, I'm now leaning toward installing two trolling deep cycle batteries. One for pure trolling and the other for starting the 20hp outboard + lights + accessories. Then, I'll have two identical batteries that could back each other up if either one becomes completely discharged.<br /><br />I am still a little concerned about my motor's alternator charging a trolling deep cycle battery. Is it considered a trickle charge or will it overload a deep cycle battery?<br /><br />What do you guys think of my proposed setup utilizing two trolling deep cycle batteries? I'm still going to check into the West Marine Combiner 150 to see if that is a direction I want to go.

 

[Ralph 123]

Re: Battered and confused about batteries

I think that would be fine. You should have no problem with your alt damaging the batteries esp if you share the charge when the motor is running. <br /><br />You may need to charge your trolling motor battery when you get home since you probably won't be running the motor long enough to compleetly recharge them both on the way in.<br /><br />Just never make the mistake of parelleling the batteries and letting your trolling motor discharge both batteries w/o realizing it (hence the combiner)<br /><br />If you don't mind charging the trolling battery when you get home you can have a battery dedicated to that and hooked up to nothing else. Then you don't need to buy a combiner or worry one bit. You could then spend that money on buying a good charger like those made by Guest.

 

[Paul Moir]

Re: Battered and confused about batteries

Good idea. Mr. Spencer has said everything and more than I would have. So, "What he said!"