agm battery charging

My lawn mower has one of these in it. I think mainly because of room and it lays down flat. I started it last night first time after it sat all winter. It was turning slow but started. Let it run some then loaded it up and hauled it home. Started right up then. I wonder if I need a special charger for these ? I might be best to just run it more and let machine do the charging ?
My go to charger for regular batteries is a small unit that I think has a desulfating mode as it charges up. I'm thinking this one will be a NO-NO on these batteries ? I also have one of the cheap harbor freight float ? chargers. It is just a little square black box with a light on it. I never trusted it to leave it on batteries real long. I don't think it really turns off. I have some larger chargers that may be over kill and kill this one ?

My motorcycle has had an AGM for the last 4 years and I charge it with a cheap little HF maintainer charger, I haven't started it yet but the headlight comes on bright, I'm sure you will get a lot more advise on this topic!

My car has an AMG. Owner's manual says charging voltage shouldn't exceed 14.8v. Should use charger designed for AMG and not to use trickle charger.

That's what GM says.

If you don't have an AMG charger use a volt meter and see if voltage exceeds 14.8.

AGM batteries need to be charged slow, because they can't dissipate the heat as well as flooded type.

The thing to avoid is getting the battery hot by pushing too many amps into it. Depending on what battery is in your mower, optimum charge rate would be 10% of the AH rating for 8-10 hours. I'm going to guess your battery has a 12-16AH rating so, 1.2-1.6 amps for 8-10 hours. I'd go with 1.5 which is pretty common on a small charger. If you MUST use 2amp, I'd do it for no more than 30-45 minutes for no more then three times with a cooling period of 1 hour between.

A trickle charger will be fine.

-Scott

This looks like some reliable info once you get beyond the advertising for their charger.

Several categories to look through. It doesn't appear any special equipment is needed, but I would be careful not to hit it with too many amps. Low and slow charging is better for any battery.

Desulfating is also good for AGM batteries, so your charger should work fine.

One thing that is cautioned against is letting an alternator bring up a discharged battery after a jump start. Though it gets done countless times a day, it has a couple of disadvantages.

One is it over works the alternator. It is only designed to maintain the charge. It is happiest when the battery is fully charged, and all it has to do is replace what was lost when cranking and overcome the normal discharge of the vehicle accessories. If it has to supply the accessory load AND bring up a discharged/defective battery, it can overheat the windings, rectifier, electrical connections, and the drive belt.

The other problem is modern alternators are very high amp output. Not like the old days when alternators were in the 30-50 amp range, the newer ones are capable of 100+ amps on some models. All the alternator knows is voltage reference. If the voltage is low, it will go full amps trying to bring it up. Back to the "low and slow", nothing low and slow when it's getting hit with 100 amps!

But, your lawn mower probably only has a very low output alternator. It may not even have a regulator, just a rectifier. It is sized to handle whatever accessory load is needed, usually just a magnetic PTO clutch and maybe some lights. The danger is starting out with a discharged battery, then loading the electrical down with the PTO clutch. There may not be enough to fully seat the clutch, it slips and overheats. Plus over working the alternator windings and rectifier.

If it had enough to start after a short run, the battery is probably still healthy. I would just put a slow charge on it until it will hold about 12.4 volts with the charger off. It should be fine.
AGM Charging

Ive owned different chargers in my RV's AND MOST USE A DIFFERENT CHARGING ALGORITHM FOR AGM VERSUS FLOODED LEAD ACID. That's NOT to say you will trash an AGM instantly overnight if the correct charger isn't used, but in most chargers I've used they have a setting and adjustment where you select Flooded Lead Acid or AGM so yes it does make a difference.

John T

Well I checked the voltage today and it was 12.8 so I best leave it alone. Letting it run while I was doing some other stuff and setting the loading ramps must of brought it up.

From what I understand you can charge an AGM with just about any automatic battery charger as long as the battery is just low and not flat dead. If it is dead like you left the ignition on for a couple of days then you will need to try charging it with a manual charger. Use a manual with a 2amp setting and leave it on for several hours till the AGM has partially recovered then put the automatic charger on. I have done that several times with pretty good success. There is something about the AGM's taking a surface charge and will fool the auto-sensing voltage limiter in battery maintainers. The other thing about AGM's is they will take all the charge you can feed into them. If you have an AGM in your car or truck and you run the battery flat dead you should charge it with a low amp 2 to 10amp charger and not just jump start the car/truck. The AGM will take the full charge from the alternator and can burn out your alternator. You basically can take an alternator and run it way past its duty cycle. Lead acid batteries don't do this.

OTJ

Most modern automatic chargers, those with a circuit board, won’t acknowledge a battery that’s connected to it that’s lower than 9 volts. We would connect the dead battery to a good one with some jumper cables to get the charger going, then disconnect the good battery.

-Scott

. Charging to such high voltages should only be a brief and intermittent occurance .
AGM batteries are best to avoid voltages over 13.8.

https://www.centurybatteries.com.au/content/documents/battery-talk/issue-2-battery-talk-battery-charging.pdf