Which amperage is best for charging? 2/10/15?

[Highcentered]

I use a regular smart charger to charge all my batteries now that my oem 5 amp 2 bank onboard charger bit the dust. It's no trouble to switch the charger over to the next battery over a couple days after a trip when I go outside for something so no plans on replacing the smart charger. Anyway, I have a group 31 Interstate agm and two group 24 deepcycles (24v xi5 doesn't use any juice hardly on my little Tracker. Also weigh A LOT less than the 27's they replaced). All 3 batteries get charged at 10a. What amperage would give me the longest battery life? Just so no one makes an assumption on agm compatibility my charger does have switchable agm mode that gets used for the agm battery.

[BMCD]

I personally will never own one over 10 amp per bank charger again.

[Highcentered]

I personally will never own on over 10 amp per bank charger again.

Do you feel a 15a put too much heat to your batteries and shortened the life? I've heard two sides of the spectrum where one side you want to get the electrolyte bubbling a little and the other side where you want to use 2a providing you have the time.

[BMCD]

Do you feel a 15a put too much heat to your batteries and shortened the life? I've heard two sides of the spectrum where one side you want to get the electrolyte bubbling a little and the other side where you want to use 2a providing you have the time.

Whatever the reason, no science behind it for me, But my batts last for 2+ years now. Course I don't keep my boats longer then that. With the 15amp chargers I was replacing a battery every year, Switched about 5 years and 3 boats ago, I think I have replaced 1 battery since then.

[CatFan]

15A. Faster charging means less time discharged. Though you often hear that low charge rates are good for batteries, you need to keep in mind that 40 or 60A are high charge rates, and 20A is a low rate.

[lpugh]

Smart chargers will adjust to the proper charge rate as needed, as cat fan stated it will bring the battery up faster. As the voltage rises the amperage will decrease to very low trickle rates, most will shut of and go into a monitor mode turning back when voltage drops. On wet lead acid batteries there used be some benefits to occasionally charging it for a few minutes at a high of charge. I think most of the smart charger now have a desulphation mode that replaces that need. I think CatFan is in the battery industry and can add to this if I am incorrect. If would not hesitate at all to use a automatic 15 amp charger

[jtracc]

Have a 15 amp per bank charger. Dual pro no issues works great going on strong no issues with batteries. Over 2 season thus far.

[Skeeterbait]

Ok, here is what I believe. In the old days, we always said a low amp charger was safer for your batteries. In the days before smart chargers with charging profiles that shut the charger down as it reached full charge, you could literally "cook" a battery by forgetting and charging it long after it had reached full charge. We basically didn't know what full charge was. So the lower amp charger was safer because it would not continue to apply high amperage to a battery after it reached full charge. Old rules are hard to break, many people believe a 2 amp charger is gentler to a battery than a 15 amp charger. But with smart chargers and automated charging profiles, that simply isn't the case any more.

The quickest death of a battery today is sulfation. In a less than fully charged battery, the sulfuric acid is unstable. Sulfur will come out of suspension and form a soft coating on the plates. This is an insulator and raises the internal resistance of the battery to recharging, and to proper discharge resulting in less reserve capacity. At first the coating is soft but if left for several months, the sulfur will crystalize and the battery will begin to die from the increasing internal resistance. But by recharging quickly after every use, and being sure to put a charger on a stored battery around once a month, you minimize the sulfation. The process can be reversed also, by charge amperage. Charging while the sulfur is till soft will melt it back into suspension in the acid. And the higher the amperage, the better job the charger will do at this reversal helping to get longer life from the batteries. In fact some chargers have a desulfate profile setting. These profiles discharge the battery, then provide a long high amp charge to reverse the soft sulfation back into the acid cleaning the plates. A modern 15 amp smart profile charger used often and properly should therefore keep your batteries better conditioned than a 2 amp trickle charger.

[InternationalMarine Brian]

Depends on how quickly you need to charge. If you want faster charge times with a 10 amp, get lithium.

[PolarKraft195]

I always liked an automatic charger, using a 10 amp charge

I've been using MK onboard chargers for the last 20+ years on my boats, with NO complaints.

[jimsch]

10 amp MK and over 4 years on Interstate batteries (?). I always check water levels and use electrical silicone on the terminals.

[FrancoCialone]

My 3-bank MK charger (5 amp per bank) is 6 years old and is still going strong. Just replaced my wet cell Dekas, (group 27) this year and got almost 6 years of service from them. They are charged in about 3-5 hours, 5 amps is more than enough for me.

[Bassmeister]

I've had a dual pro 10 amp charger for years and never a problem with batts charging overnight, usually within 2hours after a hard days fishing. I''ve had that charger for at least 10 years........

[RazorCat]

Some AGM battery manufacturers (Optima is one) don’t recommend chargers over 10 amps per bank. Personally, I’ve never had a need for anything over 10 amps per bank. My AGMs charge in 5 hours or less after fishing all day. And the higher up you go in amperage, the higher the costs of chargers. My Optima TM batteries were manufactured on 3/10, the cranking battery is 4 years old. My charger is a 10 year old Cul-M-Rite 3x10 charger.
Your money. Buy what works for you.

[JoshKeller]

15 amps per bank for me, since i do a lot of river camping and want my batteries charged asap on the shore/islands and dont want to run my generator all night.

[TritonTRXV8]

10 amps per bank has always been good all around i think. Its a double edge sword it is important to keep discharge time to a minimum but batteries get a deeper more complete charge with lower amperage.

[hunter991]

A low amp charger can have a hard time getting a a drained battery back to charge. For deep cycles and big battery's I go no less than 6 amp but my on boards are 10 amp. 6 yrs on my current batteries.

[CatFan]

batteries get a deeper more complete charge with lower amperage.

Not true.

[TritonTRXV8]

Not true.

Oh ok explain then? This is what i was taught by an old time mechanic. He always said that a battery (not fully discharded) charged at a fast high amperage rate did not get as complete of charge compared to a low amperage long term charge. Which to me always made sense. So explain to me how thats wrong then please id like to know.

[CatFan]

Oh ok explain then? This is what i was taught by an old time mechanic. He always said that a battery (not fully discharded) charged at a fast high amperage rate did not get as complete of charge compared to a low amperage long term charge. Which to me always made sense. So explain to me how thats wrong then please id like to know.

Old mechanics are the sources of a lot of misinformation about batteries. Saying a high charge current doesn't provide as complete of charge as a low charge current is very similar to saying a pot of water doesn't get as completely hot when boiled by a high flame as when boiled by a low flame.

Charging a lead-acid battery is a chemical reaction where lead sulfate is converted back to lead and aqueous sulfuric acid. Returning the sulfuric acid to the water is the reason the specific gravity of a charged battery is higher than a discharged battery. The addition of energy in the form of electricity is required in order to make this reaction occur. Because of the limits of imperfect materials, much of the energy added is wasted as heat.

By definition, a battery is fully charged when the electrolyte has been converted from water to an aqueous solution of sulfuric acid with a specific gravity that is determined by the design of the battery. Assuming you have enough current to overcome battery resistance, that sulfuric acid is generated just the same whether you are running 2A or 20A, it just happens faster at 20A than at 2A. In the latter stages of charging, charger maximum current is irrelevant. Only enough charge current as is required to maintain the charging voltage at the battery flows once the battery hits about 75% state of charge. The current continues to drop during the remainder of the charge. Most "smart" chargers stop the charge process when the current drops to 1A. This means that the end process of all chargers looks the same from a battery perspective.

Charger maximum current comes into play in a couple of areas: First, if it is too high, it can overheat the battery internally and damage the structure of the plates. If it is too low, much or all of it is wasted in overcoming battery internal resistance. Finally the rate at which the battery is charged is affected both by how much current flows during the charge and how quickly the charger is able to raise the voltage to the charging voltage. This last factor is important because the bubbling that occurs during higher rate charging is a big help in mixing the electrolyte and allowing charging to move forward more quickly.

From a battery engineering perspective, 20A is a low charge current for the typical 100AH battery we deal with. The lower charge rates are chosen because monitoring battery internal temperature becomes important when you go much higher than about 20A.