Charging deep cycle batteries

[Primitive Pete]

I have been told batteries need to be charged in the same way the current is drawn from them. Deep cycle batteries for trolling motors have a low current draw over a long time and starting batteries have a high current draw for a short time. Is it advisable to charge deep cycle batteries say at 2 AMPS and starting batteries at 12 AMPS? If so, why. What happens if a deep cycle battery is charged at 12 AMPS?

 

[JimS123]

Re: Charging deep cycle batteries

I never believe what I'm told. I try to find an expert in the field.

When the starting battery in your car or boat is recharged by the alternator, its not charging it fast at the same rate you discharged it when you started the engine. So, that in itself would be against the theory.

When I bought my new deep cycle this year I called the mfgrs. tech support line and asked them how to best charge it. They recommended an automatic charger and charge at 10 amps.

 

[LAC_STS]

Re: Charging deep cycle batteries

I had two yellow top optimas that had been sitting for about 6 mos dead. Incouldnt get them to charge.

I finally read on optimas site that batteries under 10.5 V will not charge correctly on most chargers (I tried three) and will show as bad cells on battery testers unless made for those kinds of batteries.

They said to hook them up to a fully charged battery in parallel (+ to + and - to -) and charge on 10 amps until over 11V then trickle charge until fully charged.

After I had charged them up over 11 they would read with my meter 11.55 then 11.54 and keep loosing a hundreth of a V every three secs or so. I put them on 2amp trickle for 2 days and they stopped loosing charge and are as good as new.

 

[RogersJetboat454]

Re: Charging deep cycle batteries

Absolutely nothing.

Deep cycle batteries can be charged like a normal battery. I usually prefer to start a charge on a deep cycle battery by charging them at 6-12 amps (depending on the battery charger) for a couple of hours, then switching to a 2 amp charge for a few hours after that.

It's important to note that all "deep cycle" really means in the battery world, is how much a battery can be discharged and remain in that state. A standard battery's plates will sulfate (corrode) fairly quickly if you continuously draw it down to a discharged state and leave it like that. Deep cycle batteries have thicker plates inside them to resist the corrosive effects of the electrolyte solution in a discharged state.
Usually once a battery sulfides, it becomes nothing more than a core return for a new battery.

 

[MPII]

Re: Charging deep cycle batteries

So what do you do during the winter when removed from the Boat?

 

[JimS123]

Re: Charging deep cycle batteries

So what do you do during the winter when removed from the Boat?

In the winter there is only a small discharge as the weeks go by. What I do is check them monthly and when they drop to about 12.4 volts I throw them on the automatic charger at 2 amps. They usually charge up and go to float in 15-30 minutes. In my experience, if it takes less than about 8 weeks for it to drop down to 12.4 volts again, that battery will only go one more season.

Call me cwazy, but I don't believe in battery tenders. My oldest boat battery is now 7 years old and shows no signs of needing to be replaced.

 

[JimJam]

Re: Charging deep cycle batteries

Could some please explain to me what difference the amp charge makes to the battery? For example some chargers put out 800ma and others 8 amps; other than the amount of time it takes to charge the battery, how would the amp charge affect the battery life?

 

[waterinthefuel]

Re: Charging deep cycle batteries

Well Jim I was told by a college instructor for a major appliance class (this guy was an electrical genius) that the more amps you push into a battery, no matter the size, the more you reduce the life of the battery. It's harder on a battery to charge it at 10 amps than 2. The last people I would trust to tell you how to charge a battery are the people who made it. Their job is to make sure to sell batteries, not to help you extend the life of the one you have. That's like asking a car dealership how to make your car last forever, they're shooting themselves in the foot if they really tell you good information.

I don't know if that charging thing is true, but that guy forgot more about electricity than I will ever know and most of the people on this forum will ever know so I'm not sure. It makes sense though.

Oh and get a constant amp charger, the constant voltage ones are bad for batteries. They overcharge at first and undercharge later.

I have a huge deep cycle in my boat as my only battery. No matter how hard I use it that day, I put it on my automatic charger on 2 amps and walk away. Sometimes it takes 3 hours, sometimes 8 hours, at 2 amps but its very easy on the battery.

Its really up to the user what they want to do.

 

[bruceb58]

Re: Charging deep cycle batteries

Putting 10A into a deep discharge battery is nothing. Not enough current to generate enough heat to cause any problem at all.

The best battery chargers are the 3 stage battery chargers. None of the older so called "automatic" were really automatic at all. They may reduce the charge voltage but would go down to a trickle current mode that would eventually boil off the battery. All of the modern chargers are microprocessor controlled and use set charge curves. Once the battery comes up to a certain voltage based on a current, it switches current and thus voltage cutoff point before it goes into its final maintenance mode. My 3 stage charger is on my batteries 24/7.

 

[MPII]

Re: Charging deep cycle batteries

Here's a good article -

http://www.windsun.com/Batteries/Battery_FAQ.htm#Starting, Marine, and Deep-Cycle Batteries

 

[JimS123]

Re: Charging deep cycle batteries

The last people I would trust to tell you how to charge a battery are the people who made it. Their job is to make sure to sell batteries, not to help you extend the life of the one you have. That's like asking a car dealership how to make your car last forever, they're shooting themselves in the foot if they really tell you good information.

You make a valid point, but I have to disagree somewhat. The manufacturer has a vested interest because first, they want the battery to last thru the warranty period, and next if it fails to give good service the customer probably will change suppliers for the next one.

Look at Odysey's online battery maintenance recommendations. Looks like good info to me. I'm sure if it was contrary to long battery life someone on the net would be bashing it big time and a simple google would uncover that.

 

[Silvertip]

Re: Charging deep cycle batteries

Here are some numbers to chew on:

1) A standard flooded battery can be safely charged at a charge rate of up 20% of its AHr capacity. Therefore a 100 AHr battery can be charged at a 20A rate.
2) The best chargers are "smart chargers". They know what the battery actually needs and when it needs it.
3) The charge rate applied to a battery does not significantly alter its life. Two identical batteries will have two different life cycles even if they were discharged at the same rate and charged at the same rate throughout their life.
4) A charger with a 1 amp output will take roughly 20 times longer to charge a battery than a charger with a 20 amp output. The difference in battery life is nil and probably impractical to even attempt to calculate it because of the non-related battery variables.
5) Smart chargers can be left connected indefinitely. (See #2)
6) For winter storatage there are a couple of acceptable scenarios. A) connect a float charger and walk away for the season. B) Fullly charge the battery and then top it off once a month or so.
7) Slow discharge = slow charge/high discharge = high charge is bunk. If that were the case the battery charger manufacturers would not be selling 20 and 30 amp on-board or portable chargers. Fact is if you run a small light drawing 1 amp for 20 hours you sucked 20amps from the battery. A trolling motor can do that in an hour. So in both situations the battery lost 20 amps. The charge rate is no different. A 1 amp charger will do the job but it will take roughly 20 hours to do it. A 20A charger can do the job in about an hour. The taper rate (output drop off) as the battery reaches the upper end of the capacity will prolong those numbers a bit.

 

[RogersJetboat454]

Re: Charging deep cycle batteries

I agree whole heartedly with BruceB. A 10 amp charge is really nothing for a marine or automotive style battery. Consider what the alternator would be charging a battery at. Most alternators now are rated at at-least 80 amps. Not saying that the alternator would be charging at that much, but if that alternator were charging a semi depleted battery, it would most likely be charging that battery at 20-30 amps while also supplying additional amperage for the load of the rest of the electrical needs.

Why I start a battery off at a 6-12 amp charge is very simple. If you needed to boil water, would you put your pot of water on the stove, and set it to low? Most likely not. Some people don't understand that when you're charging a battery, you're not somehow storing the voltage from the battery charger in the battery. What your effectively doing is creating a controlled boil inside the battery. When a battery gets depleted, the sulfuric acid and water start to separate, reducing the chemical reaction in the battery, which drops the available voltage/amperage. When you connect a battery charger to the battery, you create a small boil that mixes up the solution again. Thats why I start off at a higher amperage to get the battery going, then switch it down to a lower amperage to maintain the process once its going (kinda like turning the heat of the stove down to low once the water boils). Back from my trade school days, I remember my related teacher basically saying, if you could shake the heck out of a battery without damaging it, you could effectively charge the battery by remixing the electrolyte solution.

And again, back to what BruceB said, getting a good microprocessor controled battery charger takes all the guess work out of charging a battery.