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Other than speed, is there an actual difference between "maintaining" and "charging" a car battery?

Some chargers have specs/blurbs that say they're good for charging batteries with capacities up to [X] Ah, and maintaining up to a larger [Y] Ah.
I don't mind waiting more. Any reason not to use a ~1A charger instead of 3-4A?

It's often recommended not to charge at a rate more than 10-20% relative to the capacity, but one article also recommended a minimum rate of 3% the capacity (for example, 1.5A for a 50Ah battery). I'm not sure how reliable that source is.

meerkt wrote:

Other than speed, is there an actual difference between "maintaining" and "charging" a car battery?

Some chargers have specs/blurbs that say they're good for charging batteries with capacities up to [X] Ah, and maintaining up to a larger [Y] Ah.
I don't mind waiting more. Any reason not to use a ~1A charger instead of 3-4A?

It's often recommended not to charge at a rate more than 10-20% relative to the capacity, but one article also recommended a minimum rate of 3% the capacity (for example, 1.5A for a 50Ah battery). I'm not sure how reliable that source is.

The amperage of the charger determines just how fast a battery charges. Big chargers can hit 100 or 50 amps. Small, 'trickle charges' can be as low as two amps.

Maintaining a battery means the charger monitors the battery voltage, and occasionally does tests on it's capacity. A maintenance charger just keeps the battery fully charged.

Big chargers? They'll throw enough power into the battery so it actually creates hydrogen and can explode. They're professional grade stuff.

If this is for long term storage? A trickle Charger will work. I have a motorcycle with a *10* year old batter and it's still just fine - cause I kept it on a trickle/maintenance charger.

Kind of hard to know what the question is asking. Is this a traditional lead acid battery? If so, is it a sealed type, or vented? Is it for a vehicle application, a solar application, something else? Are you trying to store it between use seasons? Is the storage area being kept in a reasonable temperature range? Etc.

ludi wrote:

Kind of hard to know what the question is asking. Is this a traditional lead acid battery? If so, is it a sealed type, or vented? Is it for a vehicle application, a solar application, something else? Are you trying to store it between use seasons? Is the storage area being kept in a reasonable temperature range? Etc.

It's a car battery. If it was Lion it'd be a Tesla and he'd have extensive education on the battery.

Lead acid can be maintained by a trickle or maintenance charge. Deep cycles need warmth.

DiMaestro wrote:

The amperage of the charger determines just how fast a battery charges.

The question is, ignoring charge time, any reason a low-amp charger won't do just as well?

For example, this 1A charger spec sheet says: "Battery Capacity: Up to 30Ah, maintains all battery sizes". It could be interpreted as suggesting it's "wrong" to use on >30Ah batteries. Or the charts here. For common car battery sizes, the low-amp chargers are labeled "recommended for maintenance only".

If this is for long term storage? A trickle Charger will work.

Not storage. Occasional use when the car's unused or little used for a while.

DiMaestro wrote:

Deep cycles need warmth.

Warmth?

@ludi
Plain car batteries. The immediate one I want it for is basic lead-acid. No need to add water.
It's currently very depleted. 5V unloaded, 3V connected in the car (alarm system?).

meerkt wrote:

@ludi
Plain car batteries. The immediate one I want it for is basic lead-acid. No need to add water.
It's currently very depleted. 5V unloaded, 3V connected in the car (alarm system?).

A conventional 12V lead acid battery depleted below 10-ish volts for any length of time is guaranteed dead. A deep cycle battery will go down to around 8.5V, otherwise same rules apply.

The plates are likely sulfated, it won't come back.

ludi wrote:

The plates are likely sulfated, it won't come back.

So are chargers with a "desulfation" feature a form of snake oil?

Reading around, it's suggested it may be possible to revive, at least partially, depending on various factors?
I'm going to get a charger anyway, so won't hurt to see what happens (unless it explodes catastrophically ).

Just need to decide if 1A will do.

just brew it! wrote:

So are chargers with a "desulfation" feature a form of snake oil?

Sounds potentially doable, maybe depends on the specifics of the charger and battery?

Let me guess. Left it on the concrete garage floor for a year or so without an insulator between it and the floor. Classic car battery death cause.

Captain Ned wrote:

Let me guess. Left it on the concrete garage floor for a year or so without an insulator between it and the floor. Classic car battery death cause.

Even the best of insulators could make the battery die earlier, not later - that depends on the temperature of concrete vs. air. If you want to store a battery for months without charging, you better put it in a place as cold as possible - but keep it from freezing, of course.

Anyway, it's still better to not just leave it and forget it but check it regularly, or keep it connected to a trickle charger all the time.

https://batteryguy.com/kb/knowledge-base/how-to-store-lead-acid-batteries/

Not concrete floor for a year. Hooked in an unused car for a few weeks.

just brew it! wrote:

ludi wrote:

The plates are likely sulfated, it won't come back.

So are chargers with a "desulfation" feature a form of snake oil?

IME, no. I have an AGM battery in my kit car and it would only float charge on a standard charger / driving around. It'd die by the time I went to start the car in the afternoon if I drove it to work.

I got a smart charger instead of the "dumb" one with a desulfation cycle and it's been perfect ever since. I don't pretend to understand how it works but it absolutely did.

Captain Ned wrote:

Let me guess. Left it on the concrete garage floor for a year or so without an insulator between it and the floor. Classic car battery death cause.

Literally hasn't been an issue in a century since batteries are encased in plastic now.

Older article, but AFAIK lead acid battery tech hasn't changed too much in the intervening years:
https://www.upsbatterycenter.com/blog/battery-desulfation/

The takeaways:

1) A conventional charging cycle won't revive a sulfated battery. You may get a temporary charge into it but it won't hold.
2) A rated de-sulfating charger may be able to break down some of the crystalization by running equalizing cycles, but it's hit-or-miss as to whether the battery will be restored.

The best two things that can be done for a lead-acid battery are to never let the battery discharge past its cycle limit, and if it does, replace it.

If I remember correctly a "maintenance" charger is also known as a "float" charger.

https://www.harborfreight.com/automatic ... 42292.html

The idea is to keep the lead acid battery around 12v. So the voltage will float around this value. The charger will let the battery drop to around 11v and then charge it back up to 13v and then let the cycle begin again. Trickle chargers may or may not do the same thing as a maintenance or float charger in that they may charge the battery to 13v-14v and keep it there forever.

So far I know of these battery charger types:

Quick charge - charges the battery to 14 volts as fast as possible
boost/jump charger - charges the battery as fast as possible and may have a mode that can help just start the car with an extra 400amps+
Float charger
Trickle charger
Desulfator or pulse charger - rapidly cycles the battery between charge/discharge in the hopes of restoring the battery. The little ones you can find in the store probably don't work.
The huge commercial ones that can switch 100 to 200 amps charge/discharge DO work! I would not be surprised if those cheaper batteries "refurbed" batts in some places are just desulfated, cleaned up, water balanced and sold at a nice profit. Costs $10 to do it and you buy it for $50 to $100.

meerkt wrote:

DiMaestro wrote:

The amperage of the charger determines just how fast a battery charges.

The question is, ignoring charge time, any reason a low-amp charger won't do just as well?

For example, this 1A charger spec sheet says: "Battery Capacity: Up to 30Ah, maintains all battery sizes". It could be interpreted as suggesting it's "wrong" to use on >30Ah batteries. Or the charts here. For common car battery sizes, the low-amp chargers are labeled "recommended for maintenance only".

If this is for long term storage? A trickle Charger will work.

Not storage. Occasional use when the car's unused or little used for a while.

DiMaestro wrote:

Deep cycles need warmth.

Warmth?

@ludi
Plain car batteries. The immediate one I want it for is basic lead-acid. No need to add water.
It's currently very depleted. 5V unloaded, 3V connected in the car (alarm system?).

MeerKT - deep cycle batteries are particular about their heat range. They live/store better when they live in a warmer climate. I know it sounds goofy, but this is what my Interstate Battery dealer told me years ago - and while it may be incorrect information, it will surely allow the battery to live longer.

DiMaestro wrote:

MeerKT - deep cycle batteries are particular about their heat range. They live/store better when they live in a warmer climate. I know it sounds goofy, but this is what my Interstate Battery dealer told me years ago - and while it may be incorrect information, it will surely allow the battery to live longer.

Uhm...not exactly:
https://www.trojanbattery.com/pdf/WP_DeepCycleBatteryStorage_0512.pdf

Without getting into the many corner cases, a pretty good rule of thumb with most chemical batteries is that they store best when cool and work best when warm, and hate extreme temperatures either way. Since it's impossible to satisfy all those conditions at once, lifespan can be all over the map depending on application.

ludi wrote:

DiMaestro wrote:

MeerKT - deep cycle batteries are particular about their heat range. They live/store better when they live in a warmer climate. I know it sounds goofy, but this is what my Interstate Battery dealer told me years ago - and while it may be incorrect information, it will surely allow the battery to live longer.

Uhm...not exactly:
https://www.trojanbattery.com/pdf/WP_DeepCycleBatteryStorage_0512.pdf

Without getting into the many corner cases, a pretty good rule of thumb with most chemical batteries is that they store best when cool and work best when warm, and hate extreme temperatures either way. Since it's impossible to satisfy all those conditions at once, lifespan can be all over the map depending on application.

Aye. Perhaps I wasn't explicit - cold means -30F. I'm from ND/MN +20 is a warmer climate.

Sorry for the confusion.

I agree with Ludi. Car batteries last longer in the northeast than they do in south Florida.

The battery is basic, not deep-cycle. But it won't have to wait long for the moment of truth; the charger should be here in a few days.

I decided to go for a 3A one, if nothing else for its extra "repair" mode. Hooray for market segmentation through firmware. (Okay, maybe a few beefier components.)

BTW, right after disconnection the battery was 5V, a day later 8V, now 9V.

meerkt wrote:

BTW, right after disconnection the battery was 5V, a day later 8V, now 9V.

"Recovery voltage" is a common phenomenon for an unloaded unit. As long as there is exposed plate lead anywhere in the cell, and acid of sufficiently low pH, the chemistry still wants to make around 2V/cell. But if you load it and it immediately drops, then there isn't much going on in there.

I imagined it's something of the sort. Never scrutinized a battery like I did this one, so it's the first time I noticed.

Anyway, after a full charge of some 20 hours, 13.1V.
I let it sit for a day, 13.0V (unloaded).
30 mins of city driving including 3-4 starts, I think it was 12.8V (loaded, car off).
I let it sit for an hour, 12.9V.

Not sure what's the actual capacity now. I'll keep a close watch the next few weeks.

The charger, BTW, starts with a basic desulphation phase, but it spent practically zero time there. I don't know if suggesting the battery is in a better condition than I expected. Sadly, turned out the charger does not have a dedicated repair mode, which was the reason I chose it. Somehow in my shopping research I failed to notice that it's only available in sibling models.

meerkt wrote:

I imagined it's something of the sort. Never scrutinized a battery like I did this one, so it's the first time I noticed.

Anyway, after a full charge of some 20 hours, 13.1V.
I let it sit for a day, 13.0V (unloaded).
30 mins of city driving including 3-4 starts, I think it was 12.8V (loaded, car off).
I let it sit for an hour, 12.9V.

Not sure what's the actual capacity now. I'll keep a close watch the next few weeks.

That's a surprisingly good result. Hope it holds.

The acid test (pardon the pun) will be a period of cold weather. Look for trouble when winter comes around. If it's still working fine, you're golden.

So far, workable.

The car only saw light city usage these last 2 months.
I've charged the battery twice, whenever it dropped to ~12.3V loaded, car off (I think that's 12.45V unloaded).

Longer term report:

Battery still seems fine. In periods of time with less driving I charged once a month. Not otherwise.

(There were a handful of unexplained starting problems, but I suspect the starter.)