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Salvaging "Dead" Absorbent Glass Mat Batteries

Posts: 55
Location: Valley City, ND.
urban solar greening the desert
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So as I have mentioned elsewhere, I have a procedure to salvage AGM batteries.  These are the kind you find in UPSs, alarm panels and those emergency lights that only come on when they power goes out.  I am NOT an electrical engineer, though my Grandpa use to run the little kiddy mine railroad out in Calico, near Barstow. And I do have a fair amount of experience, especially with these smaller batteries.    

That in no way makes me a qualified expert at anything, so before I explain the procedure, a word of warning.

Please DON'T Kill Yourself.

If you have no understanding of which end of the screwdriver to turn, then you should likely not read any further!  Yes, I am being facetious, but I am being truthful too.  If you can't approach this procedure with caution and the proper protections, than please don't read any further.  You need eye protection most of all.  You need old clothes too- battery acid LOVES cotton.  Cotton does not like battery acid...  If you get some on your skin, you won't burst into flames, I assure you, but you should wash with plenty of water and soap right away.  Wearing gloves is obviously the thing to do.  

In addition, working with batteries is dangerous.  You could conceivably start a fire, because batteries do emit hydrogen.  Don't smoke or put these batteries atop your Rocket Mass Heater to work on them, etc.  Honestly, if you take a simple amount of caution, you will be fine.  These batteries are so small and the technology so advanced in age, that it's easier to crush your toe with one than to actually make it explode or spray acid.  That reminds me, no hip sandal wearing.  If you do drop one or manage to otherwise have a hazard occur, full shoes will protect you much better.

So what is an AGM, Sealed Lead Acid battery?  AGM stands for "Absorbent Glass Mat."  Essentially, it's a woven structure that absorbs the water and sulfuric acid into the mat, thereby meaning the battery can be laid on its side and not leak water.  That's why it's called a Sealed Lead Acid battery- there is no way for the water and acid to leave the battery.  It also means, there is no way for the user to maintain the battery- or is there?

On the AGM SLA battery below, notice the cover atop?  See how it goes all the way around?  Well that's "removable."  You can pop it with a tiny flat bladed screwdriver.  It's glued all the way round with little dollops of super glue.  So move slowly, find the dollops and get as close to them as you can with the screwdriver.  Otherwise, you may crack the lid and you have an unusable battery now.  

Once you get the lid off, it will look like the one below.

Notice the little rubber caps atop the battery?  If you have ever worked with a standard car battery, they will be immediately obvious to you as the cells of the battery.  GENTLY pry them off with your finger atop them.  The reason is, a battery "breathes."  In certain situations, it can have positive pressure.  As the rubber cap nears the top, it can fly off.  So keep your finger atop as you "pop" it.  Trying to find one of these buggers after they go careening off into space is really tough.  In fact, you will learn to save the extras to batteries that are unsalvageable for this express purpose.  Save a couple of lids too- sooner or later you will break one.

Now that you have the caps off, look down into the cells with a flashlight.  Can you see water?  If you can, great.  That means the battery is most likely still in good shape.  The water should just cover the top of the white glass mat.  It should just cover it though.  If you can't see it, it's is a sign that the battery needs water.  It's possibly a sign that it's dead too, but your charger will likely tell you that.

Word of warning-  NEVER use a straight manual charger with these AGMs.  They HATE being over charged, like every other battery does.  But these really dislike it, to the point that they will bulge, even break and spill acid.  Plus, a manual charger just pushes electricity.  In a situation where a battery has high resistance, the whole thing turns into the chocolate candy conveyor scene from I Love Lucy.  Except it's not so funny when the battery is actually sizzling, acid is spilled all over your bench and you have a real mess to clean up...  Always use an automatic charger.  


I highly recommend you buy that same charger as mine.  In fact, I don't know what in the heck I ever did without one.  Goodness knows how many good batteries I wasted...  They are seriously inexpensive too!  And it charges lithium, NICAD, LIPO and any other battery you can think of.  I got it to extend the life of my drone batteries- but man was it a bargain.  It charges standard lead acid batteries of all types.  And you can use it with one battery to charge another!  I use to bring an AGM SLA in the car, hook it up to that and then charge my three volt drone batteries with it.  Can't say enough good about this little bugger.

The charger is around $38 and is called the SKYRC iMAX B6 Mini.  I bought mine from Amazon.  Below is a picture of the charger and all the really super useful stuff you get with it.  For small solar arrays and UPS\alarm\motorcycle\lawn mower and even car batteries, this charger is awesome.

Now time to add water.  I use a 10 CC syringe.  I have a 50 CC, but with small batteries like this, the 10 CC seems to be better.  Suck up as much DISTILLED water as possible in the syringe.  Why distilled water?  Well I have gotten in a number of arguments with people who claim that tap water is fine.  They claim that the mineral content in tap water is really low, not enough to make a difference.  Well the people who make these things don't use tap water.  So for the whole dollar it costs for a gallon of distilled water, why argue?  

Put the tip of the syringe into the cell's hole and start filling.  Go slow- you don't want to squirt water out once it is filled.  The more syringes full a battery takes, the more likely it is that it is dead.  But even four or five syringes full -a bone dry battery- has come back to 90% or better.  Miracles do happen.  So for a small effort, it's worth trying on every battery.  When full, the water will bubble out the top of the cell you are filling.  At that point, pull the syringe out and go on to the next cell.  Now a word of warning while filling.  You want the syringe to gently rest in the cells hole.  That way when it bubbles out, you don't end up squirting it all over your clothes.  Fill each cell to the point where it bubbles out the top.  Then go back to the first cell put the syringe back into it.  Pull back sharply on the plunger.  This will suck the excess water back into the syringe.  Squirt that into a glass and pour it down the drain and rinse.  

The reason that's important is that too much water in a cell dilutes the strength of the cell.  Let it sit for say 15 minutes, then check to make sure the glass is still submerged in water.  If you find a cell not submerged, fill it again.  This is because the glass mat is thirsty, absorbing the water back into the mat.  Wait 15 more minutes and fill as necessary until every cell stays full.

Ok, now I put the battery on that little miracle charger I mentioned earlier at a very low amperage.  I like to use 0.5 amps.  (Half an amp.)  Why?  Because this is the battery equivalent of a blood transfusion.  We want to work with the anemic patient carefully.  We want to give them time to get back up and around.  So take it easy on the poor thing.  

But what about those rubber cell covers?  Should we not put those back?


The reason is, the battery will pass a lot of gas, so to speak, in the charging process.  If you put them on, the pressure will build and they will go flying off, never to be found again.  So take a folded up paper towel and place it over the top of the cell.  It will let the battery pass gas and any excess water will be caught by the towel.  Make sure the towel does NOT touch the terminals of the battery.  It is, in theory, possible for the acid water to cause a short between the terminals.  Never seen it happen but why take chances?

Now turn on the charger.

One of two things will happen.

Either it will sound of a warning "tune" and show "CONNECTION BREAK" on the screen or it will start its charging cycle.  What's a connection break?  Well either you did not hook the wires up solid like or the batteries internal resistance is soooooo high, that the charger won't be able to charge it.  Check the connections and try again.  If it comes up with "CONNECTION BREAK" again, STOP.  It's dead, time to recycle.  The internal resistance is so high that the charger won't even try it.  The charger is wiser than you.  Use the charger.  I tried charging a battery once that I thought was fine.  I KNEW my RC charger was smoking crack... turned out I was.  I FORCED it to charge with a manual charger.  Came back later to find my lab bench sprinkled with battery acid and the sides of the battery bowed out so much that I was afraid the thing would burst open.

Trust the charger.  The charger is wise, kind and loving.  The charger is all knowing and wants to be your friend.  Trust the charger and take its advice.  The charger only wants to protect and prosper you.  When you know the wires are connected properly and you still see "CONNECTION BRAEK," recycle the battery.

Ok, so let's say the charger blesses your battery and starts charging.  You may hear some fizzy type noises coming from the battery.  That's normal.  The battery will heat up too.  That's normal.  The slight bit of excess water in the cells will dampen the towel, that's normal too.  The charger will run for a bit, an hour I think and then sound an alarm.  The screen will say, "END TIME" meaning the charger charged as long as it could at the amperage you said and simply ran out of time.  (I think it's an hour?)  When you hear the alarm, examine the battery again.  Is it super hot?  I mean like you could fry an egg hot?  Toss it into the recycle pile.  

Go back through the check and fill cycle again, refilling any cells that are below covering the glass mat.  Then charge the battery again using the same settings.  Once you see that all the cells are full after a small charge cycle, you can boost the charge to one or two amps.  I never charge more than two amps at a time, usually just one amp.  Slower is better when charging friend.    

The "All Blessed & Wise Charger" knows when the battery is fully charged and will terminate the charge early at some point.  When it does, it will display the final charge voltage.  Usually, it's something like 14.2 Volts or there about.  So now disconnect the battery and do one final water level check.  If the cells are all submerged with water, congrats, you salvaged the battery!  Well maybe not.  You should wait two hours and let the battery settle in to its fully charged state.  Anything over 12.8 volts on a meter I consider to be 80 to 90% of life.  Anything over 13 Volts is 90% or better.  Again, these are rough estimates learned from charging a LOT of old AGM SLA batteries.  I am not an electrical engineer and most of them will say I am a nut.  But the police, fire and city\county governments love me.  They use these recovered SLAs sometimes for years.  I have built a 12 Volt battery array for my emergency light and charging stations.  I am planning on putting together a salvaged 12 volt motor home water pump with a solar charger and salvaged battery array to pump water in case the power goes out in a long term emergency.  (A few years back, a huge flood came through and knocked the power out.  City water was shut off.  My place has a naturally filling cistern.  With it, the solar charger and battery array, I can still flush the toilets and wash the dishes.  Half of surviving any disaster is in keeping sanitary.)

So if the battery still needs water, you should refill and go back to the half amp charge.  Follow through with that same cycle from earlier until the battery won't charge very long AND it maintains water levels above the glass in EACH cell.  It's pretty much full at that point, as full as practical anyway.  

Now it's time to put the little rubber caps back on each cell.  Then put the cell cover on the top.  You can glue it back, but why?  It just makes it harder to take off again.  I tend to use thick wound tape from the first aid kit and tape it down as in the pictures.  (Appropriate, no?)  The other advantage is you don't clog the gas channels on the battery.  Use just tiny drops of glue if you do glue the lid back.  The one exception to tape is if the batteries will be exposed to weather.  The tape will rot away with wind and rain and sun and those rubber caps will force the lid off and go flying about.  Below is a pic of a dead battery that I used in this demo.  I got two years out of it in my garden, running a pump for my Small Scale Growing experiments.

When in use, I pop the top off and check the water levels on every battery about every three months.  When in storage, I do that once every six months.  As a battery cycles, it will slowly "eat" water, just like your car battery.  So sooner or later you will have to refill.  I put each battery through the cycle above again, just to be sure.  And I toss it if the great and wise charger says, "CONNECTION BREAK."

"Sounds like a lot of work for a worn out battery!"  

Not really.  It takes less than 15 minutes of actual time to do the whole thing- per battery.  (As in total time.  It can take up to six hours of charge time to salvage a battery- but you don't have to stand and watch.)  A new battery is $15- without shipping!  I get mine hand delivered by companies wanting to get rid of them.  I recycle the ones I can't salvage- and get good money in return!!!      

Questions?  Just ask away.  


Oh, and my obligatory "accidentally took a picture of the wall" pic included for fun.

Post Script

So how many batteries are really salvageable this way?  A surprising number.  Roughly half.  Are they like new?  No.  But for nearly all small applications, they are more than sufficient.  For instance, the local police\fire\medical people love me.  Like most of America, our power system are becoming less and less reliable.  (There are some very good, oddly competing ideas why that is- but that's for the cider press.)  Small government entities, even the National Guard unit here in my town, simply don't have the money to buy this kind of stuff.  So when they are given a salvaged UPS with a salvaged battery that has a two year life span left in it, they are appreciative.  Especially the first time a lightning bolt has everyone around them gritting their teeth and cursing Zeus- but their computer is fine.  So what if they only get seven minutes of time to shut their computer down gracefully?  Who needs a full ten minutes to shut down a computer anyway?  We all hate to see taxes rise, so you might say I am doing a bit to keep everybodies taxes down.  

And they work great running a 350Ma pump in my small growing system, which I shall now shamelessly plug.  Head over to Https://VerticalFarmMechanics.com and take a look at my vertical growing system, won't you?  Sign up for my mailing list and if you like what you see there, well why not join my test team?  All you have to do is tell me what you learned from my system and where it can be made better- and I will send you a free one to try out!

You can also message me with one of those "Purple Moose-ages" these folks have around here and get in touch that way.
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