battery question

[MASTERBrian]

I am looking to buy a new battery for my pontoon. It has a 50hp Johnson on it. It's also setup with a spot for a trolling motor. It has a spot for two batteries, so I'm sure I'll go that route eventually and use a large deep cycle for the troller. The question is on the starting/Normal use battery, am I better off actually buying a starting battery or am I also ok if I go with a larger deep cycle battery. This battery will of course start the motor, but run bilge pump for a slide and/or live well, lights, radio, ect. Kind of curious pro/con of either option. My understanding is either will start that small motor without issue, and MY logic tells me a large deep cycle should give me more float time, motor off, lights on and radio going than just the start battery. Is that good logic or bad. Is it worth the extra cost?

 

[bruceb58]

A deep cycle battery will start that motor easily as well.

 

[airshot]

A deep cycle would be your best bet, the only negative with a deep cycle is that they like to be charged slowly. I am quite sure your 50 will not charge it to fast, however on inboards or autos the alternator is capable of fast charging which can lower the life expectancy of a deep cycle. While not a drastic drop in life it is noticeable. The stator on your 50 should not put out a high enough charge to cause any problems with a deep cycle. If you do choose to go with an electric troller
then by all means get a second battery, I would not trust my main starting battery to run an elec troller and still have a safe amount of starting power left.

 

[Silvertip]

Slow charging is not especially true. Trojan is one of the better known deep cycle battery manufacturers and they (as well as other manufacturers) recommend charge rates up to 10 - 13% of rated capacity but the battery can safely handle charge rates of up to 20% of rated capacity. Most modern smart chargers charge in three stages where the initial charge is at a high rate. Then there is an intermediate rate and finally a maintenance (very low) charge rate. If one attempted to charge a deep cycle battery at a 1.5 - 2.0 amp (slow charge) rate it would take days. Most of the bottom end smart chargers on the market have a charge rate of 5 or 6 amps and the higher end, multi-output units run 6 - 20 amps per output. These smart chargers take all the guesswork out of battery charging.

 

[smokeonthewater]

Just bite the bullet and do it right now.... Get a normal size starting batt for the engine and a big deep cycle for lights, pumps, tunes, and future trolling motor. Also snag an onboard charger.

 

[oldjeep]

Just bite the bullet and do it right now.... Get a normal size starting batt for the engine and a big deep cycle for lights, pumps, tunes, and future trolling motor. Also snag an onboard charger.

x2. Since you only need to charge the troller it is pretty easy to wire up and then you just need to run an extension cord (attached to a GFI outlet) down to the boat rather than pulling the battery out.

 

[bruceb58]

Deep cycle batteries can be charged at the same rate as a starting battery. I have never seen any documentation that says otherwise.

I have used deep cycle batteries to start the 7.4L in my boat. If it can start that, it can start a 50HP Johnson outboard.

 

[H20Rat]

Deep cycle batteries can be charged at the same rate as a starting battery. I have never seen any documentation that says otherwise.

I have used deep cycle batteries to start the 7.4L in my boat. If it can start that, it can start a 50HP Johnson outboard.

exactly! I use all deep cycle batts in my motorhome, a group 27 deep cycle starts a carbed big block ford 460 without issue. Current boat has a single deep cycle to start the mercury v6 sportjet as well as power a large stereo.

 

[airshot]

Deep cycle batteries can be charged at the same rate as a starting battery. I have never seen any documentation that says otherwise.

I have used deep cycle batteries to start the 7.4L in my boat. If it can start that, it can start a 50HP Johnson outboard.

Interesting.....every deep cycle battery manufacturer I have looked up recommends not using high output alternators to get maximum life from the battery. In all the cases I have read it states for longest life expectancy from a deep cycle battery use a slow charger designed specifically for deep cycle batteries. I will bet my money on the manufacturers recommendations thanks.

 

[airshot]

The reference to slow charging of deep cycle batteries is in regards to an automotive type alternator charging system. Having looked up a number of deep cycle manufacturers they have all stated" for maximum battery life use a slow charger designed for deep cycle batteries", "the high rate of charge from automotive type charging systems can shorten the number of charging cycles and the overall life expectancy of a deep cycle battery". My two cents is bet on the manufacturers recommendations............

 

[bruceb58]

The reference to slow charging of deep cycle batteries is in regards to an automotive type alternator charging system. Having looked up a number of deep cycle manufacturers they have all stated" for maximum battery life use a slow charger designed for deep cycle batteries", "the high rate of charge from automotive type charging systems can shorten the number of charging cycles and the overall life expectancy of a deep cycle battery". My two cents is bet on the manufacturers recommendations............

Put in a link that shows this information.

What manufacturers did you look up that state this?

 

[airshot]

I have a walmart deep cycle that states that in the instructions as well as Interstate, dura last from autozone and deep cycle batteries from the andersons and the deep cycle batteries from tractor supply, and cabela's and from bass pro shops. I think those are enough to make my point. Just read the instruction tag that comes with the batteries. I stated his 50 hp OB should be perfectly safe charging a deep cycle battery, it is the automotive type alternators of 45 and 60 amps and above that will shorten the battery life/cycles.

 

[airshot]

This new format is a pain, 45 minutes to post a simple reply..... bruceb58..not going to get into an argument over this but...I have a walmart deep cycle that states in the instructions just what I have posted and so does Interstate batterys, so does auto zone Duralast batterys, so does Anderon's batterys, so does tractor supply batterys, so does bass pro shops and so does Cabela's deep cycles batterys. His 50 hp OB will be fine, it is the automotive typs alternators that are the problem,
like some used in inboard engines.

 

[airshot]

Sorry for all the double posting but the site tells me that it can't post my replys so I redo them and it posts them twice.........can't wait to get the bugs out!!

 

[smokeonthewater]

I've bought a LOT of batteries and NEVER even heard of one coming with instructions other than motorcycle size batts having instructions on how to fill em with acid and charge for the first time?????

 

[H20Rat]

You guys are making mountains out of molehills...

First question, how much amperage does a 50 amp alternator put out at 14.4 volts? (I'll give you a second to think about that, continue reading when you have answer...)

Hint, if you answer 50 amps, you are wrong. SAE J 56 specifies alternator ratings are at 13.5 volts. Problem is, lead acid's won't even charge at 13.5 volts. In reality, the only amperage used to charge a battery is what is available at 14.4 volts. Drop below that, and the alternator output means NOTHING, it won't be going into the battery. If you measure the actual charging current going to a battery (which I have, on numerous vehicles), it is shockingly (no pun!) small! Alternators in general make pretty crappy battery chargers.

So yes, you can recharge deep cycles with a big alternator, I'm on the same deep cycle house battery on my RV, going on 6 years now... Alternator hanging on the front of that engine is around 140 amp.

(disclaimer, SAE J 56 is an international spec dictating how to measure alternators, it's not impossible to find non-spec alternators, although I doubt they would be common place in a marine environment.)

 

[bruceb58]

I've bought a LOT of batteries and NEVER even heard of one coming with instructions other than motorcycle size batts having instructions on how to fill em with acid and charge for the first time?????

Agreed. I have never seen any either and that is why I was welcoming viewing a link on a battery site...any battery site!

I have Oddyseys in my boat and they specifically say on their website that a rapid charge is not an issue.

I agree with Smokingcrater. Nearly all motorhomes use deep cycle battery banks for their house batteries and all of these get charge off the engines high output alternator.

 

[dingbat]

I run twin grp. 27 AC Delco voyagers on my boat. One as a starting battery and one on a ACR for house. My outboard has 60 amp output. Get 5-6 years out of a battery which is good enough for me. Messing with battery chargers suxs

 

[oldjeep]

I run twin grp. 27 AC Delco voyagers on my boat. One as a starting battery and one on a ACR for house. My outboard has 60 amp output. Get 5-6 years out of a battery which is good enough for me. Messing with battery chargers suxs

Chargers are easy, you just mount it in the boat.

 

[Idlespeedonly]

Agreed. I have never seen any either and that is why I was welcoming viewing a link on a battery site...any battery site!

I have Oddyseys in my boat and they specifically say on their website that a rapid charge is not an issue.

I agree with Smokingcrater. Nearly all motorhomes use deep cycle battery banks for their house batteries and all of these get charge off the engines high output alternator.

My inverter charges the house batteries.