Maintenance Free Lead Acid Battery

What does "Maintenance Free" mean to you?

I do some electrical maintenance on school buses. Big diesel engines with very large and heavy 12 volt batteries - two in each bus in parallel. Many of them have "Maintenance Free" on their labels. Those that I've looked inside of are "what I think" is low on electrolyte, but enough is in there to have the plates covered. Haven't added any distilled water as I'm not sure it's needed with the "Maintenance Free" label.

Comments welcome and thanks.

From my EXTREMELY LIMITED understanding, sealed lead acid batteries (ie, maintenance free) are simply batteries that are sealed to prevent the normal Joe Schmoe from having to check electrolyte levels. However, they ARE able to lose gases due to venting, such as when recharge state creates too much pressure inside the battery -- again, as I understand it, from charging too rapidly. Venting pressure now and then ends up leaving the battery a bit low on electrolyte.

I've seen videos where people have drilled through the housing, replaced electrolyte, then sealed their holes. Seems I also saw one where a guy was able to pry the top completely off of the battery, then replaced it later. In all instances, those batteries were shown to be bad, so nothing to lose.

There's an interesting article on Wikipedia about batteries:
https://en.wikipedia.org/wiki/Lead–acid_battery#"Maintenance_free",_"sealed"_and_"VRLA"

In the article, it states this:
[i:9f434e52d4][b:9f434e52d4]Valve regulated (VRLA)[/b:9f434e52d4]
In a valve regulated leadacid (VRLA) battery, the hydrogen and oxygen produced in the cells largely recombine into water. Leakage is minimal, although some electrolyte still escapes if the recombination cannot keep up with gas evolution. Since VRLA batteries do not require (and make impossible) regular checking of the electrolyte level, they have been called maintenance free batteries. However, this is somewhat of a misnomer. VRLA cells do require maintenance. As electrolyte is lost, VRLA cells "dry-out" and lose capacity. This can be detected by taking regular internal resistance, conductance or impedance measurements. Regular testing reveals whether more involved testing and maintenance is required. [color=blue:9f434e52d4][b:9f434e52d4]Recent maintenance procedures have been developed allowing "rehydration", often restoring significant amounts of lost capacity.[/b:9f434e52d4][/color:9f434e52d4]

VRLA types became popular on motorcycles around 1983,[27] because the acid electrolyte is absorbed into the separator, so it cannot spill.[28] The separator also helps them better withstand vibration. They are also popular in stationary applications such as telecommunications sites, due to their small footprint and installation flexibility.[29][/i:9f434e52d4]

Sure would like a little more info on the part in [b:9f434e52d4][color=blue:9f434e52d4]BLUE[/color:9f434e52d4][/b:9f434e52d4].

If the plates are covered you're okay.
If there is a loss of electrolyte, it would most likely be caused by over charging. Either over charging by the onboard changing system or from someone connecting an external charger.
Generally the charging voltage should not exceed 15 volts on a 12 volt battery.

There's nothing wrong with adding a little distilled water to a maintenance-free battery. If you don't, it will eventually run low on electrolyte. Maintenance-free batteries are supposed to not need water for their expected life. But that life will probably be a little longer if you add water.

In my casual relationship with the dozen or so batteries in my equipment, there are 2 types of "sealed" batteries: One with the caps that can be removed even though they say to leave them alone, and the other with some kind of mesh in the venting system which has no visible means of looking into the cells to check the fluid level. On the ones that I can get to and pry the caps off, I have never had to replace any fluid and it's usually roughly half way or higher between the top of the plates and the "full" indicator.

As I recall, a big motivator in the switch to maintenance-free batteries was people's habit of topping off batteries with tap water. In most parts of the country, this would lead to an earlier battery death than if they'd just left them alone.

My understanding, if the only difference is a lack of access due to no fill caps, it is no different than any other lead acid battery.

Some have cleverly hidden flush with the top caps that can be pried out.

But typically, a battery in normal use will not need to be refilled. In fact, what I have found, trying to keep one full to the bottom of the fill ring indicators will result in the top staying wet, and the terminals constantly corroding. This is especially true in off road, marine, and hard riding trucks where there is a lot of bouncing around. Best to let them seek their own level as long as the plates are just covered, and they may even be visible, right at the surface.

Then there are the totally sealed types, AGM, gel batteries. Those are not to be serviced or disturbed in any way.

Hello 55 50 Ron,

I say leave them alone, as you have not stated that they are failing a load test. Have you checked the individual cells voltage?. Electrolyte level changes with the state of charge and temperature.
More when the battery is being charged, and usually spills out if they are overfilled,

Guido.

I have the original battery in a Kubota M6800 that dates back to 2001. It works flawlessly but has never been1)accidentally discharged; (2) Is disconnected when not being used for more than a week; (3) Is inside a dry shed but not removed from tractor, temperature will get down below freezing most winter days and sometimes go to minus 30F; (4) Before starting on cold days the engine is warmed with factory block heater and charger is hooked to battery. Charger "start" mode is used while cranking, engine starts on first rev; (6) No maintenance charger, no removing battery to store in warm place. Nineteen years.

Oh, I forgot. In addition to the above, battery has never been opened. I don't even know if it can be opened, I have no idea how much electrolyte is in it and I don't care. As long as it works. Only problem is, where do I get another one like it?

A lot of them mean reduced maintenance. Those just seal a little better but eventually you will have to pop the caps off and add water especially when they start to get old. Then there are those that don't have any caps to remove.

If you can get fill caps off. Add enough distilled water to cover the plates by 1/4"

There are 2 advantages of a "Maintenance Free" battery. 1. It's just that "Maintenance Free". You are not suppose to get to the cells. 2. They are AGM. They are sealed so no battery acid fumes can escape and cause oxidation of cables. If no acid fume can escape there should never be a reason to add water.

AGM, "Maintenance Free" batteries are the only thing I'll buy. My car's owners manual says not to replace battery with anything but an AGM. The engine stops at stop light and the AGM battery is designed to handle the restarting better than a conventional wet cell.

Don't over think it, "Maintenance Free" battery is just that "Maintenance Free".
geo.

Sorry. I didn't fully state enough details. Also some didn't fully read the subject line with "Lead Acid Battery" stated.

These batteries are not AGMs. They do have screw out caps to view the cell's electrolyte level. I didn't do any load tests.

Thanks for all your responses.

(quoted from post at 15:33:21 03/01/20) There are 2 advantages of a "Maintenance Free" battery. 1. It's just that "Maintenance Free". You are not suppose to get to the cells. 2. They are AGM.

Click to expand...

All AGM batteries are maintenance free, but not all maintenance free batteries are AGM.

Agree! As long as your voltage regulator is working properly, really no reason to have to add water......distilled water.....like you mix with your antifreeze! I just wish I could feed my household hot water heater distilled water. We are heavy alkali here making for nice showers and no iron rust and all in the sinks, but eats up the water heater every 6 years, regardless of type, quality. Suckers are up to 600 bucks these days for LP. Geez!

(quoted from post at 18:33:21 03/01/20) There are 2 advantages of a "Maintenance Free" battery. 1. It's just that "Maintenance Free". You are not suppose to get to the cells. 2. They are AGM. They are sealed so no battery acid fumes can escape and cause oxidation of cables. If no acid fume can escape there should never be a reason to add water.

AGM, "Maintenance Free" batteries are the only thing I'll buy. My car's owners manual says not to replace battery with anything but an AGM. The engine stops at stop light and the AGM battery is designed to handle the restarting better than a conventional wet cell.

Don't over think it, "Maintenance Free" battery is just that "Maintenance Free".
geo.

Click to expand...

Not every "Maintenance " Free " battery is AGM .

What does AGM mean?

Absorbed Glass Mat batteries