I've got an old Sears car battery charger. 2A/10A variety. Nothing too fancy. The manual says when you hook it up, you should see a lot of current flow, and when it's charged, the current will have dropped to less than half the selected flow. So when it's fully charged, ir should be less than 5A.

I put it on 10A and hooked it up, and I'm seeing something just above 2A. But the car had to be jumped just a few hours ago. So, does this just not work right for AGM batteries? Of did the car miraculously recharge the battery in the 40 minutes I ran it?

I should note the battery is probably quite cold. I thought perhaps that's the issue. They say not to charge a frozen battery in the manual, but hell. How they hell would you avoid that when it's 5 degrees out?

Might be time to consider upgrading your charging equipment to something like a NOCO Genius battery charge/maintainer like this:

https://www.amazon.com/NOCO-GE...o+%2Caps%2C96&sr=8-9

I have an earlier version that we use on various cars that aren’t driven frequently. Just hook it up and forget it.

quote:

Originally posted by smlsig:
Might be time to consider upgrading your charging equipment to something like a NOCO Genius battery charge/maintainer like this:

https://www.amazon.com/NOCO-GE...o+%2Caps%2C96&sr=8-9

I have an earlier version that we use on various cars that aren’t driven frequently. Just hook it up and forget it.

Ordered!

I pulled that one off because I was afraid of the unknown due to the anomaly. But I suspect that just the best flow you get when it's under 5 degrees outside. We're back up to warmer temps by mid-week. I'm thinking the battery shouldn't be shot. It's only 4 years old, and was (theoretically) a good one.

If your "old" charger is whats now considered a "dumb" charger I would hang onto it. The newer "smart "chargers won't charge a badly depleted battery. You need to jump the battery with another to build up enough charge so the "smart" charger can ID the battery and then charge it.
I hang onto my old dumb charger, its what I go to first.
Charging characteristics between a wet cell and a AGM are very close.

You keep a battery from freezing by keeping it charged. A fully charge battery will freeze somewhere south of -60, but a fully discharged battery will freeze somewhere north of 10 degrees.

If your battery was frozen, you needed to take it in the house to thaw, then charge it. AGM battery chemistry is exactly the same as a regular lead acid battery. No special charger is needed. However, due to the differences in construction, an AGM battery can accept a little more current than a regular lead acid battery, so you could, but it’s completely optional, get a special charger to charge an AGM battery a little quicker.

If your battery was frozen, you have to figure out why it was so discharged to begin with. Without and obvious answer, ie you left the lights on, the battery itself may be bad.

I noticed the same thing with a similar charger on a OEM VW battery (type unknown). On the old wet cell lead acid batteries the current would be high for a while, then gradually dwindle to a trickle. The newer tech. batteries seem to need/have a different charging profile. Presumably, the chargers sold now are designed to take this into account, but how do they know what kind of battery they are hooked up to?

My old tech charger was not at all successful at charging the VW's failed battery, nor was my old-style trickle charge "maintainer" even when left on overnight. Excessive cold was not an issue in this case, although when it warmed up for a few days while I was dealing with this, the battery gained enough power to start the car. Note that the charging system in the car did not charge the battery very well either although I am not sure I drove far enough to really be able to tell.

The development of automotive battery technology over the past decade or so seems to have left me in the dust. Before, there was a "car battery" that was pretty much the same from all manufacturers and would work in your car, as long as it was the right group number. Now there seem to be a half dozen or so different battery technologies (wet, AGM, VRLA, SLA, EFB, etc.) each needing a different charging profile, and differing in other important ways. I am not talking about EVs, or lithium-ion batteries, these are the different ways that lead acid batteries are constructed.

Hey r0gue

since we own the same car, I may be able to help you out here. The Noco Genius line of chargers work perfectly on the X3's AGM battery.

The biggest trick to charging the current M40i is that you have to disable the hybrid battery by leaving the hood up when you charge. Also - I've found that locking the doors and moving the key away from the vehicle before initiating the charge process makes things work more smoothly.

quote:

Originally posted by teombe:
Hey r0gue

since we own the same car, I may be able to help you out here. The Noco Genius line of chargers work perfectly on the X3's AGM battery.

The biggest trick to charging the current M40i is that you have to disable the hybrid battery by leaving the hood up when you charge. Also - I've found that locking the doors and moving the key away from the vehicle before initiating the charge process makes things work more smoothly.

Thanks, but my X3 is fine. This is my 1998 Mercedes E430 V8 that my kid drives to/from his job.

quote:

Originally posted by trapper189:
You keep a battery from freezing by keeping it charged. A fully charge battery will freeze somewhere south of -60, but a fully discharged battery will freeze somewhere north of 10 degrees.

If your battery was frozen, you needed to take it in the house to thaw, then charge it. AGM battery chemistry is exactly the same as a regular lead acid battery. No special charger is needed. However, due to the differences in construction, an AGM battery can accept a little more current than a regular lead acid battery, so you could, but it’s completely optional, get a special charger to charge an AGM battery a little quicker.

If your battery was frozen, you have to figure out why it was so discharged to begin with. Without and obvious answer, ie you left the lights on, the battery itself may be bad.

I really don't know if the battery was frozen. But it was pretty dead.

AGM and lead acid take almost the same charging profile. If either is stone cold dead, they will only take about 2 amps for several hours before it jumps up to 10 amps........Charge it overnight and then have it tested. Any auto parts store tests them for free.

quote:

Originally posted by jimmy123x:
AGM and lead acid take almost the same charging profile. If either is stone cold dead, they will only take about 2 amps for several hours before it jumps up to 10 amps........Charge it overnight and then have it tested. Any auto parts store tests them for free.

Oh, that is very helpful! The manual scared me into thinking I was somehow damaging it, and I figured since I didn't know anything of AGM, I best be cautious, so I stopped.

It was totally only 2 amps. I'll hook it up again and give it several hours.

My father always said that once a battery (lead acid type) freezes it junk most of the time. That has been my experience over the years.
Dad always said that a frozen battery can explode if you try charge while frozen. I haven't tried to charge one to find out.

Let me add to the wisdom already given.

Most cars are not set up to charge (from alternator output) AGM batteries which require a higher voltage. 14.6 – 14.8V. The result is they never charge to full capacity. Depending on the vehicle there are ways to increase the alternator output, some with a simple fuse like plug in to reprograming of the ECU. Constantly not charging to full capacity will degrade the battery prematurely and give less than 100% deep that storage AGMs are favored for. Some people faced with this simply put the battery on a charger maintainer once a week or so and that works fine but it's a bit of a PITA. They sell little maintainers that mount inside the engine compartment which then only requires lifting the hood and plugging it in, making this less of a PITA.

Also, modern charger/maintainers have a "repair" selection which helps when you have a dead or almost dead battery. The one you ordered calls it "force mode" so you're good to go.