Need help choosing a battery

[Atvguy]

Hi everyone! I googled "how to charge AGM" and this was the first REAL site on the list (not counting reddit, quora, and youtube), and I found a lot of good discussion on batteries so I decided to sign up and get some personalized advice. (I would have commented on some older threads but they all seem locked.)

My situation is I have an ATV and do a lot of winching and I'm tired of replacing batteries. I'm currently using two U1 size batteries (aka lawnmower size), which is about as big as I can fit in the modded compartment. I think that size relegates me to the 35ah variety, at best. 10% of that is 3.5 amps, which I guess is the recommended charging amperage. Max is usually something like 10 amps for a deep cycle AGM.

The problem is my alternator will surely throw 20 or more amps at a battery that was drained by a 100+ amp winch. Other than turning on the headlights after I'm finished winching, I have little control over how many amps my alternator will try to charge the batteries. On top of it, I have a beefed up regulator that will handle 50 amps.

So my question is what battery and battery chemistry should I choose that would handle that scenario the best? I know it's not good for any battery, but what battery would survive the longest being drained by a winch and then being charged with a lot of amps?

There is so much conflicting info online. Some sites say AGM can't handle more than 10 amps charging and others say they can handle more than SLI. I hate to ask for help if I could figure it out on my own but I can't tell what I should believe.

 

[jhellwig]

Do you leave it running while you winch? That alone will help. Charging an agm “properly” isn’t that big of deal as long as you are charging it. Fully charging and maintaining is where the charging cycle differs a little but not enough to loose sleepover.

 

[SC Maintenance]

Alternators with voltage / charge profiles for lead acid don't work amazingly well with AGM batteries. The charge profile is different.

I have learned that in the case with my truck. Now I can make it work in my truck, because I drive long distances so its lower charge voltage will get it there eventually. I also put it on a float charger once in a while to actually get it fully charged. However if your not planning to put your ATV on a float charger frequently, I would likely stay with lead acid.

 

[Atvguy]

Do you leave it running while you winch? That alone will help. Charging an agm “properly” isn’t that big of deal as long as you are charging it. Fully charging and maintaining is where the charging cycle differs a little but not enough to loose sleepover.

Yes I leave it running and usually give it a bit of throttle. The repair manual says it's a 200w alternator which implies about 15 amps, but I have reason to believe it can do more, but it's not much compared to what the winch is drawing. Essentially the winch is running on the batteries, and then the alternator charges them back up.

What made sense to me was the explanation that the fiberglass mat in the AGM acts as a thermal insulator, which is the reason AGM is sensitive to overcharging. It makes sense, so is it true?

Alternators with voltage / charge profiles for lead acid don't work amazingly well with AGM batteries. The charge profile is different.

I have learned that in the case with my truck. Now I can make it work in my truck, because I drive long distances so its lower charge voltage will get it there eventually. I also put it on a float charger once in a while to actually get it fully charged. However if your not planning to put your ATV on a float charger frequently, I would likely stay with lead acid.

Oh you're saying the alternator never fully charges AGM? I hadn't thought of that. AGMs come stock with every ATV nowadays so I don't know how they handle that, or if they do. People report having good luck with AGMs on ATVs but they don't run winches like I do.

 

[oil pan 4]

Hi everyone! I googled "how to charge AGM" and this was the first REAL site on the list (not counting reddit, quora, and youtube), and I found a lot of good discussion on batteries so I decided to sign up and get some personalized advice. (I would have commented on some older threads but they all seem locked.)

My situation is I have an ATV and do a lot of winching and I'm tired of replacing batteries. I'm currently using two U1 size batteries (aka lawnmower size), which is about as big as I can fit in the modded compartment. I think that size relegates me to the 35ah variety, at best. 10% of that is 3.5 amps, which I guess is the recommended charging amperage. Max is usually something like 10 amps for a deep cycle AGM.

The problem is my alternator will surely throw 20 or more amps at a battery that was drained by a 100+ amp winch. Other than turning on the headlights after I'm finished winching, I have little control over how many amps my alternator will try to charge the batteries. On top of it, I have a beefed up regulator that will handle 50 amps.

So my question is what battery and battery chemistry should I choose that would handle that scenario the best? I know it's not good for any battery, but what battery would survive the longest being drained by a winch and then being charged with a lot of amps?

There is so much conflicting info online. Some sites say AGM can't handle more than 10 amps charging and others say they can handle more than SLI. I hate to ask for help if I could figure it out on my own but I can't tell what I should believe.

What's the max charging voltage?
How deeply are you discharging them?
Normally I recommend AGM but you might not want AGM in your case.
True deep cycle batteries aren't AGM for a few reasons.
AGM seems to need a bit higher voltage to fully charge.
14.4 is bare minimum for AGM. Even then you probably want to throw a charger on once and a while.
After a winching cycle where the batteries are depleted the batteries probably need to sit at float voltage, 14.4v for at least a couple hours.

 

[Donald]

Alternators with voltage / charge profiles for lead acid don't work amazingly well with AGM batteries. The charge profile is different.

I have learned that in the case with my truck. Now I can make it work in my truck, because I drive long distances so its lower charge voltage will get it there eventually. I also put it on a float charger once in a while to actually get it fully charged. However if your not planning to put your ATV on a float charger frequently, I would likely stay with lead acid.

The charging requirements for the basic AGMs is very similar to normal flooded battery. It's different for the high end AGM like Odyssey or Northstar or Optima. This is according to the specs I have read for chargers with options for multiple battery types.

I am not convinced the high end AGM batteries are worth the extra cost over the basic AGMs. But I am moving towards basic AGMs.

 

[Atvguy]

What's the max charging voltage?
How deeply are you discharging them?
Normally I recommend AGM but you might not want AGM in your case.
True deep cycle batteries aren't AGM for a few reasons.
AGM seems to need a bit higher voltage to fully charge.
14.4 is bare minimum for AGM. Even then you probably want to throw a charger on once and a while.
After a winching cycle where the batteries are depleted the batteries probably need to sit at float voltage, 14.4v for at least a couple hours.

"AGM seems to need a bit higher voltage to fully charge." That is what's really confusing me because AGM has a lower internal resistance which means if a higher voltage is applied it would draw more amps, which would then overcharge the battery.

I'm starting to think there are some poor choices of wording on some websites for how to charge AGMs which is leading to the confusion. It could be that AGMs need current limiting while still supplying a fairly high voltage, not that AGMs need a high voltage per se. The only reason to ever NEED a high voltage is to overcome a high resistance.

Conventional chargers can go as high as 17 volts, which is too much for AGM because of its lower resistance. AGMs have fiberglass separators, which are good thermal insulators. Lots of amps + poor thermal conductivity seems like a bad idea. https://www.interstatebatteries.com/blog/how-to-charge-an-agm-battery

Yuasa says AGM can't be installed in a system that was designed for conventional, presumably because the regulator would supply too many amps. The regulator would have to be redesigned to limit the amps in order to run AGM.

How deeply are you discharging them?

I have a 5000lb winch on a dump trailer that lifts about 1000-1500lb of dirt with a pole and pulleys. I'll dump a load then drive back to the dig site and reload. I'll do that over and over many times in a day.

I'm not sure how deeply the batteries discharge but there is never an issue restarting the ATV after a dump cycle. It seems like the ride back is sufficient to charge them back up. But I can say the winch struggles quite a bit for the better part of a minute, and then has to let the trailer back down.

I don't do that all the time. Most of the time I'm just riding like a normal ATVer or the ATV is parked for a couple months. Oddly enough, it's usually during those "normal" times when the batteries fail.

 

[Atvguy]

The charging requirements for the basic AGMs is very similar to normal flooded battery. It's different for the high end AGM like Odyssey or Northstar or Optima. This is according to the specs I have read for chargers with options for multiple battery types.

I am not convinced the high end AGM batteries are worth the extra cost over the basic AGMs. But I am moving towards basic AGMs.

I wouldn't mind dropping $300 on a battery that would last, but for the same amount I can get ten $30 batteries from Walmart.

One of the batteries sits on the back rack and is simple to swap out, but the other one is buried under the front rack. I have so many connectors on it I have to take a pic so I know how to put it back together. I'd gladly pay extra not to have to go through that anymore.

 

[fantastic]

"AGM seems to need a bit higher voltage to fully charge." That is what's really confusing me because AGM has a lower internal resistance which means if a higher voltage is applied it would draw more amps, which would then overcharge the battery.

I'm starting to think there are some poor choices of wording on some websites for how to charge AGMs which is leading to the confusion. It could be that AGMs need current limiting while still supplying a fairly high voltage, not that AGMs need a high voltage per se. The only reason to ever NEED a high voltage is to overcome a high resistance.

Conventional chargers can go as high as 17 volts, which is too much for AGM because of its lower resistance. AGMs have fiberglass separators, which are good thermal insulators. Lots of amps + poor thermal conductivity seems like a bad idea. https://www.interstatebatteries.com/blog/how-to-charge-an-agm-battery

• Not exactly sure what you meant to say but higher voltages produce lower amperage draws.
• AGM's have a slightly higher charging profile. For example an old wet battery you'd want to float at 13.2v while AGM you can float at 13.4v-13.6v.
• If you're concerned about the vehicles charging system overcharging the AGM then you need to buy a DC to DC AGM battery charger.

I have 5 year old AGM's in the basement that are floated at 14v. I don't know what their capacity is right now but they're still holding some power. These are on my battery backup sump pumps so they need to have full power at all times so a bit more extreme floating voltages.

 

[Atvguy]

Not exactly sure what you meant to say but higher voltages produce lower amperage draws.

I could be wrong but here is my reasoning:

V=IR so if V is constant and R declines then I must increase.

Let's say if a regulator is trying to achieve 14.4v across 1 ohm resistance then the current it would output is 14.4 amps. But if the resistance were cut in half to 0.5 ohms then the current would double to 28.8 amps.

So a battery with less resistance will draw more amps from the charging system in order to achieve the same voltage.

Maybe what you're trying to say assumes constant power, not constant voltage. If power is constant then higher voltage means lower amps.

Here's how Interstate Batteries put it:

AGM batteries don’t have nearly as much internal resistance, which is how they absorb 30, 40, even 50 amps at a time instead of a regular battery getting stressed out at more than 10 amps.

This is also why an AGM battery needs special charging.

Regular battery charging can break AGM batteries. Regular batteries need 15-17 volts to get the same amps. However, voltage greater than 15 volts can overheat an AGM and generate enough pressure to pop its safety valve. That one-way valve is supposed to relieve excess pressure from the harmless gases that come when a battery’s charging. Too much voltage becomes too much pressure, and pop. Without an airtight seal, an AGM will dry out in hours.

 

[SC Maintenance]

I could be wrong but here is my reasoning:

V=IR so if V is constant and R declines then I must increase.

Let's say if a regulator is trying to achieve 14.4v across 1 ohm resistance then the current it would output is 14.4 amps. But if the resistance were cut in half to 0.5 ohms then the current would double to 28.8 amps.

So a battery with less resistance will draw more amps from the charging system in order to achieve the same voltage.

Maybe what you're trying to say assumes constant power, not constant voltage. If power is constant then higher voltage means lower amps.

Here's how Interstate Batteries put it:

You were given the answer by @fantastic above. V=IR. If voltage increases with constant resistance current drops.

They don't charge correctly at a Lead acid voltage, and its not constant - it has a profile, depending on where in the charge cycle it is I believe the higher voltage has something to do with the electrolyte, but I am not sure - I am not a chemist.

Why do you think high quality battery chargers have different settings for lead acid and AGM?

Anyway, a regular charger will get you to about 80% charge +/-. Maybe that is high enough. Are you sure your current batteries are failing from low charge? Might be failing from vibration?

 

[Atvguy]

You were given the answer by @fantastic above. V=IR. If voltage increases with constant resistance current drops.

They don't charge correctly at a Lead acid voltage, and its not constant - it has a profile, depending on where in the charge cycle it is I believe the higher voltage has something to do with the electrolyte, but I am not sure - I am not a chemist.

Why do you think high quality battery chargers have different settings for lead acid and AGM?

Anyway, a regular charger will get you to about 80% charge +/-. Maybe that is high enough. Are you sure your current batteries are failing from low charge? Might be failing from vibration?

The constant voltage I'm referring to is my alternator regulator that will always try to achieve 14.4-14.7. If the resistance drops because I switch from SLI to AGM batteries, then my charging system will output more amps in its effort to raise the voltage to 14.4-14.7. Those extra amps may overheat an AGM, hence the warning from Yuasa.

I think you're spot on about vibration killing my batteries. I had the same suspicion because it's always the battery on the rear rack that fails. I didn't want to complicate the discussion with that variable yet. AGM is absolutely the best battery for vibration, but if SLI is the best for winching then maybe I can find a robust SLI or I can find a new spot to put the battery.

 

[fantastic]

I could be wrong but here is my reasoning:

V=IR so if V is constant and R declines then I must increase.

Let's say if a regulator is trying to achieve 14.4v across 1 ohm resistance then the current it would output is 14.4 amps. But if the resistance were cut in half to 0.5 ohms then the current would double to 28.8 amps.

So a battery with less resistance will draw more amps from the charging system in order to achieve the same voltage.

Maybe what you're trying to say assumes constant power, not constant voltage. If power is constant then higher voltage means lower amps.

Here's how Interstate Batteries put it:

The resistance would include the wiring to the battery as well. This site suggests no more than 30% so for a 35Ah battery that would be 11.4A charge.

https://discoverbattery.com/support/learning-center/battery-101/how-to-charge-an-agm-battery

The constant voltage I'm referring to is my alternator regulator that will always try to achieve 14.4-14.7. If the resistance drops because I switch from SLI to AGM batteries, then my charging system will output more amps in its effort to raise the voltage to 14.4-14.7. Those extra amps may overheat an AGM, hence the warning from Yuasa.

If resistance is reduced b/c you're switching from SLI to AGM then amperage should drop as well b/c the Voltage will increase due to the lower resistance. If we're speaking about one source of power from your alternator. If you went to some super duper thick, short, wire then maybe you could see a noticeably bigger increase but how much in the real world from the same power source? I don't know. You mention you'll have around 15A to charge.

I think you're spot on about vibration killing my batteries. I had the same suspicion because it's always the battery on the rear rack that fails. I didn't want to complicate the discussion with that variable yet. AGM is absolutely the best battery for vibration, but if SLI is the best for winching then maybe I can find a robust SLI or I can find a new spot to put the battery.

Get an AGM not only are they better at vibration they have a better load handling than wet lead acid. I'd try to fit the biggest battery you can. When you're not riding put it on a tender.

 

[SC Maintenance]

AGM's have a higher over voltage required to get full charge. Simple ohms law formula isn't going to solve this for you.

As mentioned, AGM's are better with vibration - that is why I went to one in my truck. I also put a 1/8 inch sheet of heavy silicon rubber gasket material under my batteries. Seems to help dampen the vibration - or maybe its just placebo that makes me feel better?

 

[Atvguy]

If resistance is reduced b/c you're switching from SLI to AGM then amperage should drop as well b/c the Voltage will increase due to the lower resistance.

Voltage is always the same because it's designed into the regulator to keep it at 14.4-14.7. The only thing that can change in response to reduced resistance is current.

Actually, adding a 2nd battery reduces resistance because it's in parallel. 1/R = 1/R1 + 1/R2. In response the alternator should put out more amps, not less.

Now AGM worries me more because if I had two of them it would really strain my charging system. I just realized that. Two AGMs in parallel could be bordering on a short circuit.

I'd try to fit the biggest battery you can.

I'm going to look into that but I doubt there is much I can do because the shock towers are in the way.

Ideally I'd want a deep cycle marine flooded battery but they don't make them that small. Anything deep cycle and that small is AGM.

 

[Atvguy]

AGM's have a higher over voltage required to get full charge. Simple ohms law formula isn't going to solve this for you.

As mentioned, AGM's are better with vibration - that is why I went to one in my truck. I also put a 1/8 inch sheet of heavy silicon rubber gasket material under my batteries. Seems to help dampen the vibration - or maybe its just placebo that makes me feel better?

1/8 isn't much but I'm sure it helps some. What might help the most is putting it in the center of your truck, closest to the center of mass.

Imagine if you had your battery on the back bumper of your truck lol. That's closer to what I'm dealing with. I picked the absolute worst spot to put a battery.

 

[SC Maintenance]

1/8 isn't much but I'm sure it helps some. What might help the most is putting it in the center of your truck, closest to the center of mass.

Imagine if you had your battery on the back bumper of your truck lol. That's closer to what I'm dealing with. I picked the absolute worst spot to put a battery.

Sounds like your dealing with shock (sudden non repetitive force) rather than vibration (repetitive oscillation, like from a engine or driveline). Both can have problems. I used 1/8 inch because I have limited overhead space, and also I was simply trying to disrupt the vibration repetion. We use special types of foam in the industrial world, but its very expensive so I figured I would try the high density silicon. In your case if you have the overhead space you might want to try something like this?

 

[Atvguy]

Sounds like your dealing with shock (sudden non repetitive force) rather than vibration (repetitive oscillation, like from a engine or driveline). Both can have problems. I used 1/8 inch because I have limited overhead space, and also I was simply trying to disrupt the vibration repetion. We use special types of foam in the industrial world, but its very expensive so I figured I would try the high density silicon. In your case if you have the overhead space you might want to try something like this?

I'm not sure if it's shock or vibration. I don't know how to tell. All I know is the front battery outlives 2 or 3 back ones, so it got me thinking. Also not sure if I want to spend $300 on a battery and have it shaken apart too.

About a week ago I noticed the batteries getting weak but thought it was because I'm running 5 lights and doing a lot of start n stop so the batteries never have a chance to charge back up. So I put them on the charger and they seemed better for a couple days. Then I parked one night and came back out to completely dead batteries.... both of them... just from being parked one night. I tried charging them back but they just kept sucking charge and never topping off.

So I separated them and charged the back battery only. The next day the back battery measured 8 volts. The front measured 10 after NOT being on a charger all night. Ok, so the back battery is junk. I put the charger on the front battery and it seems ok. I'm still using it now to start and drive around. It's damaged, but holds a charge all night and starts with plenty of power the next day. I can still use it until I decide what to do next.

So the back battery died and then it damaged the front one. Being 8 volts makes me think something inside came apart.

The quad weighs 900lbs and has super stiff shocks so it rides like a log wagon.

But this still doesn't mean I absolutely need AGM. I designed the back battery to come off easy. It has a quick release clamp, so just unplug it and carry it to a campsite. If the battery is getting damaged from shock I could always unplug it and not use it until I need it for winching. Just riding around I only need one battery. Not being on the quad is probably the best protection there is

The foam might help if I make a sandwich out of it with a piece of wood or something on top to keep the battery from wearing through it. I don't know how much it would help though.

 

[oil pan 4]

"AGM seems to need a bit higher voltage to fully charge." That is what's really confusing me because AGM has a lower internal resistance which means if a higher voltage is applied it would draw more amps, which would then overcharge the battery.

I'm starting to think there are some poor choices of wording on some websites for how to charge AGMs which is leading to the confusion. It could be that AGMs need current limiting while still supplying a fairly high voltage, not that AGMs need a high voltage per se. The only reason to ever NEED a high voltage is to overcome a high resistance.

Conventional chargers can go as high as 17 volts, which is too much for AGM because of its lower resistance. AGMs have fiberglass separators, which are good thermal insulators. Lots of amps + poor thermal conductivity seems like a bad idea. https://www.interstatebatteries.com/blog/how-to-charge-an-agm-battery

Yuasa says AGM can't be installed in a system that was designed for conventional, presumably because the regulator would supply too many amps. The regulator would have to be redesigned to limit the amps in order to run AGM.

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I have a 5000lb winch on a dump trailer that lifts about 1000-1500lb of dirt with a pole and pulleys. I'll dump a load then drive back to the dig site and reload. I'll do that over and over many times in a day.

I'm not sure how deeply the batteries discharge but there is never an issue restarting the ATV after a dump cycle. It seems like the ride back is sufficient to charge them back up. But I can say the winch struggles quite a bit for the better part of a minute, and then has to let the trailer back down.

I don't do that all the time. Most of the time I'm just riding like a normal ATVer or the ATV is parked for a couple months. Oddly enough, it's usually during those "normal" times when the batteries fail.

I didn't mean go to a higher voltage and ram more amps through the battery. Where I work we pretty much only use AGM. Peak voltage on the chargers is 15.1v but they're amp limited to 20 amps so they don't charge at 15 volts all the time and they're thermally protected while charging. Limit the amps to whatever that battery recommeds.
17v is fine for a deeply discharged AGM battery as long as the amps and temperature are limited.
It sounds like deep cycling the battery.
What are you doing mining?
At some point during your digging and driving cycle you need to stop everything for a half hour at least let the batteries rest and check voltage. You could have a battery with 11 volts start your ATV just fine. You may need to switch to a true deep cycle battery or at least a deep cycle marine battery either way sounds like you definitely need a bigger battery.
Also when paralleling 2 batteries they need to have matching resting voltage. Say one battery has a resting voltage of 12.3v and the other one is 12.8 the higher battery will lose a good portion of it's charge though the weaker battery. Best to go with 1 big battery or two 6 volt batteries in series.

 

[oil pan 4]

The constant voltage I'm referring to is my alternator regulator that will always try to achieve 14.4-14.7. If the resistance drops because I switch from SLI to AGM batteries, then my charging system will output more amps in its effort to raise the voltage to 14.4-14.7. Those extra amps may overheat an AGM, hence the warning from Yuasa.

I think you're spot on about vibration killing my batteries. I had the same suspicion because it's always the battery on the rear rack that fails. I didn't want to complicate the discussion with that variable yet. AGM is absolutely the best battery for vibration, but if SLI is the best for winching then maybe I can find a robust SLI or I can find a new spot to put the battery.

AGM seems to be the best in a vibration application.
I'm putting an AGM on a stump grinder that will be the ultimate test and I'll know soon enough.