How a lead-acid battery works

How a lead-acid battery works

How a lead acid battery works EngineerGuy Series #4
The increasing amount of technology we rely on in
everyday life makes portable energy sources essential
to our world today.
We can power our cellphones and laptops with
lithium ion batteries, run flashlights from alkaline ones,
and many of our watches depend on batteries constructed with silver oxide.
This one, though, may be the most important of them all.
Now I know it seems a clunky, old-fashioned thing
it was invented in the 19th century
but it still makes our world move by starting our
cars, motorcycles, and trucks.
No wonder it’s the best selling battery.
If you understand how this battery operates
you can grasp the principles underlying any of the newer ones
and even see why no single type of battery can be used in all applications.
Let’s take a look inside.
The first thing to note about this motorcycle battery is that it’s heavy
That’s because it’s tightly packed with lead and lead oxide sheets
both of which are very dense.
This is a cell from an identical battery
and you can see the lead and underneath this the lead oxide.
They alternate throughout the interior.
So, let me show you how they store electricity using just two plates.
So, I have here a lead plate and a lead oxide plate from the battery
and the sulfuric acid.
And now watch what happens when I connect the leads
The LED lights up.
A current flows from the lead oxide cathode to the lead anode.
The lead gives up electrons, which the lead oxide accepts.
This exchange turns both plates into solid lead sulfate.
Now let me measure the voltage difference between the two leads.
And you can see that it’s about two volts
which means that to make this 12-volt battery
six cells are linked in series to make up the 12 volts.
So, that’s the basic electrochemical reaction
now let’s look at how you engineer a battery.
We want a battery to have a high density of either energy or power.
That difference being that batteries with a high energy density
can store large amounts of energy,
and release it reliably over long periods of time,
whereas batteries with a high power density release
large amounts of energy quickly.
This battery was designed with power in mind
because we need a burst of nearly four hundred amps to start a motorcycle.
To save space we need to pack the plates in here tightly
but in order to ensure that the electron transfer
takes place through the terminals
the plates are mechanically separated by these permeable layers.
Now, let me show you two plates from a discharged battery
so you can see the effect of a deep discharge of a battery.
If we look at these two plates we can see
the effect of a long term discharge.
This light coating here is lead sulfate.
That explains why if you run a car battery to zero charge
a few times you’re likely to kill it.
As the battery discharges, lead sulfate cakes the space between the plates.
If too much builds up, you’ll never be able to recharge the battery.
This highlights how every different application
needs a different type of battery.
You see with most engineered objects
there are going to be trade-offs
giving away some characteristic you want
to gain others that you must have.
Indeed, the toughest part of engineering often ends up
being balancing the trade-offs in a design.
For example, a car battery does a great job starting a vehicle
but not running one, like an electric car.
Nor is it a good candidate to store energy
from solar panels in a house.
There we harvest energy from the sun
charge up the batteries
and then use the stored energy
in a variety of ways until the batteries die and
then recharge them with the sun’s energy.
For this use you would use what is called a deep cycle battery.
As the name implies this battery’s capacity can be largely used
and then recharged easily.
To convert an SLI battery
like used to start a motorcycle or a car
into a deep cycle battery we do three things.
We use thicker electrodes to increase energy density
space them further apart so lead sulfate debris can fall off of them
and add room below where that debris can accumulate.
The trade off is that it’s larger, heavier
and gives off a lower current than a car battery.
It would seem that we’d want to get rid of the lead-acid battery
It poses a significant environmental risk if disposed of improperly.
We still have the 19th century lead-acid battery
because of what nature has handed us
plentiful electrode materials, lead and lead oxide
both very high in conductivity.
Once we arrange these materials correctly we have a
cheap battery with a high power density.
No other materials found in nature meet these criteria so well
which means that with current technology it is extremely difficult
to overcome this barrier.
That’s why 19th century technology is still
the go to for starting our cars.
I’m Bill Hammack, the Engineer guy.
This video is based on a chapter in the book
Eight Amazing Engineering Stories.
The chapter features more information about this subject.
Learn more about the book at the address below.

100 Replies to “How a lead-acid battery works”

  1. From the above explanation, it seems as though lead batteries could be reused if they were made to be opened so the user could wipe the plates off periodically.

  2. So why do people think lithium batteries will replace old acid batteries, and furthermore why are lithium batteries reacting so violently. I have seen more runaway lithium batteries than I have seen corroded nickle-cad or alkaline batteries.

  3. Hi,
    I am Cheng Chin Pong. I am a science teacher from Taiwan. I like this video very much, but I noticed there are no traditional chinese subtitle in this video, so I translate that and submit to your website. But there is still no tradition chinese subtitle.

  4. Des O'connor
    Dionne Warwick
    Cash Managment Banking
    Version 1.1
    Date Produced
    09th September 2016
    Prepared by
    Marek Rakowski
    Trainer and Learner Development Consultant

  5. Hey bill love the videos, keep up the great work! Just out of curiosity have you ever heard anyone call it Lead Peroxide instead of just Lead Oxide? Can't seem to find a clear answer on the internet. Also in deep cell batteries they use a lot of sponge lead, I also come from an automotive background not an engineering one. Again great videos!

  6. can you go indepth into how a battery can STORE a charge? im still confused by it. i can understand how electricity is carried, but how does lead hold the electricity in place?

  7. He needed to remind how properly dispose of the battery too, because people throw them in the total waste which affects groundwater.

  8. How exactly does a lead acid battery work? How exactly does a rainbow work? How exactly does a posi-trac on a Plymouth work?…… It just does!

  9. Good on ya mate, well done. The perfect balance of complexity and time. Would love to see scope and sequence across other battery systems like LiPo for my students – and myself! Keep up the great work, and the books too!

  10. I really wish i had professors like you when i was in college getting my engineering degree. I probably would have gone MUCH farther in my engineering career than I am now if my teachers showed the same enthusiasm as you. I appreciate all these videos you make

    My teachers were more focused on their research versus teaching their students :/


  12. It's not necessarily the greenest battery when thrown in the garbage but just about every store that sells these batteries must recycle the old ones, that is why you're charged a core deposit fee if you don't have the old battery. Once you bring back the old one, they refund you for the core deposit. There are also newer versions of this lead acid battery known as Absorbed Glass Matt (AGM) and we're now seeing lithium ion, the same type of battery found in your smartphone. AGM is an improvement in capacity and cranking power as well as longevity and typically comes with a much greater warranty usually about 4-6 years. They require less maintenance and don't have any free flowing acid which means there's no need to check for the acid levels in the cells and no spillage. The downside to the AGM battery is that if you discharge them too much they're harder to bring back, they're heavier, and they're more expensive. Then there's lithium which provides even better results than AGM batteries but in a much lighter package. There's a certain BMW M model that uses one and some stores sell lithium powersport batteries found in motorcycles, ATVs, dirt bikes, and jet skis. They're often times more expensive than AGM batteries but have an even longer life cycle but must be pulse charged and require a lithium ion rated charger. If you use the wrong charger it could damage the battery and lithium can be a volatile substance as we've seen in the Galaxy Note 7 if not properly charged or maintained.

  13. engineerguy blows my mind. He's the kind of person who whilst growing up just wanted to know how everything worked. So he found out.

  14. Is a lead acid battery consider a wet cell battery ? My dad is traveling with his electric wheelchair but the airline doesn’t allow wet cell batteries.

  15. Why would a "deep cycle lead acid battery" with thicker electrodes spaced farther apart with a cavity to collect debris give out "less current" ? I agree that it would be heavier and larger, but give less current too? WHY???

  16. Please answer my question :
    At the cathode end there is always electrons leaving battery continuously or it started after we connect wire? ☺🙋

  17. This is a really great explanation! I love how you clearly explained how to 'convert' a motorcycle battery to a solar battery. It is simple but doesn't dumb it down. I need this in my class.

  18. In stationary applications where weight and size aren't much of an issue, lead acid batteries offer the lowest levelized cost of stored energy of any of the chemistries. Lithium based chemistries have a longer cycle life, but not enough more compared to upfront cost. Lead Acid isn't going away anytime soon. some batteries, with tubular cathodes have cycle lives in the thousands. A good forklift battery can give a levelized cost of less than $.08. Lithium, about $.12. (cents per Kilowatt Hour).

  19. Engineerguy pointing at lead acid battery while shoving away the lithium ion one:
    " This might be the most important one of them all"

    Lithium ion : "Hold my battery water.."

  20. For ICE starting, a heavy lead battery can be replaced with a much smaller secondary battery like LiFePO4 & a 6S supercapacitor bank of a few hundred farads.

  21. Is it true that ALL batteries are technically in theory rechargeable (even alkaline) since all chemical reactions are reversible if you add energy back into them (or pull energy out) ?

  22. I would love to learn how to developed a battery especially on how to create a Laptop battery and make it last longer

  23. ………hi folks,,, Remember lead is poisonous. If you got to pull a battery apart although it's best not to , you need to be mindful of the lead dust that might collect on your hands and clothing and anywhere else. Then it should be disposed of thoughtfuly.

  24. Just came upon your site, in that I'm thinking of changing out my Motorhome batteries as well. I've got 4 golf cart 6V batteries, thinking of going with AGM this time. Wondering if I should add two more ( ) as I have a residential fridge that tends to pull out many Ah's from my system. I'm new to this lifestyle, so a ton to learn…nothing for wifi or cell boosting yet, so as I say, lots to learn.

  25. Why do you say that the current flows from the cathode to the anode? Don’t electrons flow from the reducing agent (anode) to the oxidizing agent (cathode)?

  26. Is this true as I heard that lead acid battery creats high voltage at time of cranking engine ,that other can't!??? please give explaination

  27. excellent production, greatly informative. I completely agree regarding "natures gift" to us. Simple, clear, well done.

  28. It's not just automobiles, but powering high drain devices such as computers. Anyone who lives in an area with a not so reliable grid, or invested over $1000 into a desktop should have one. Even if they can only sustain 15 minutes of their maximum load, this is more than enough time to ensure a proper shutdown.

  29. lead acid battery coming back because of cheap availability … for instant charging by remove and refilling the electrolyte system will coming in future .. electrolyte station will be there instead of petrol / gas station … no need to wait charging … only need the battery have a outlet and inlet where electrolyte remove and pump back to battery .. full charge immediately station

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