How Does A Lead Acid Battery Actually Work?

We all know what batteries are and what they do for us, but how exactly do they work? What exactly is a “lead acid” battery?

Lead Acid Battery

There are lots  of new different battery technologies coming into the mainstream such as lithium batteries so are lead acid batteries still of any use or are they obsolete? How do they compare to other types of batteries?

An electrical battery is combination of two or more “cells” which are used to convert chemical energy into electrical energy. A battery stores electricity and creates voltage from the chemical reaction produced when two different metals are immersed in an “electrolyte solution”.

Within the battery, a chemical reaction occurs and electrons move from one pole to to the other and the different metals and and electrolytes used give the battery differetn characteristics, the most important of which is the varying voltage of the battery.

How It Works

So, batteries are made up of cells and lead acid batteries contain lead grids onto which lead and nother plate fof lead oxide are pasted with a sulphuric acid alectrolyte that the plates are all immersed in.

The lead combines with SO4 (sulphate) to create PbSO4 (lead sulphate) and creates a free electron. Lead dioxode, hydrogen ions and SO4 ions, along wityh electrons from the lead plate create PbSO4 and water on the lead dioxode plate.

As the battery discharges both plates build up PbSO4 and water builds up in the acid. The voltage is about 2.2 volts per cell so for car starter batteries that most people know, 6 of these plates are connected in series (which adds voltages and keeps the same amps) to produce a 12 volt battery (technically actually 13.2 volts).

This reaction is reversible, so if you apply current to a battery at the correct voltage, lead and lead dioxode form again on the plates, enabling you to reuse the battery until the active material has been depleted, which leaves the battery unsuable.

There are clearly a finite amount of sulphate ions in the acid and the available surface of area of the lead it bonds to is limited as well. Therefore as the sulphate is depleted the voltage becomes weaker.

Self Discharge Of Lead Acid Batteries

One mildly irritating side effect of lead acid batteries is that the chemical reaction between the lead and the sulphate ions cannot be completely stopped. This menas that the battery continues to discharge even when they are not in use.

We have all come back to a car after a holiday or long period of storage and found it will not start!

Lead acid batteries tend to self discharge at the rate of approximately 1% per day althoughthis can vary depending on various factors. Oddly perhaps, the warmer it is the faster the rate of self discharge.

Particularly with car batteries, trivial power draw such as internal lights or the radios can take a tiny amount of power even when apparently turned off – we’ve all done this with left on lights.

Why Does My Lead Acid Battery Die?

So, why does a lead acid battery stop working? And generally at the worst possible time….

Partial Discharge

As the battery discharges, it lowers the amount of electrolyte solution (the sulphuric acid mixed with water) and this leaves the lead plates partially exposed.

If the plates remain exposed the suplhate that is already bonded to the lead can harden and will then remain on the lead permanently weakening the battery’s ability to recharge.

This partial discharge is a common problem with car and boat batteries that are not used and recharged often enough.

Deep Discharge

Another common cause of battery death is deep discharge, particularly in the marine environment. For most lead acid batteries this is taking a battery below 50% charge.

At this point, small pieces of the lead plates can actually break off and sink into the electrolyte solution leaving less material available for the chemical reaction with the suplhate ions. Obviously if too much breaks off then the reaction simply cannot happen.

Once this has happened, although you can for example jump start your car, the damage is done and it will never hold the same charge and will need replacing.

This is the key problem faced by people using them in the marine environment, where you need to get back to shore in tough conditions and completely run the battery down. Do this a few times and the battery will need replacing very quickly.


This occurs when you keep charging a battery that is already full. Doing this can break down the material of the electrolyte which will leave no sulphate left to bond with the lead.

This is why you should never leave a lead acid battery permanently on charge unless you are using a smart charger that is specfically designed for this purpose eg leaving your classic car on charge over winter ready for the spring.

Are Lead Acid Batteries Obsolete?

Surprisingly as a business that doesn’t sell lead acid batteries, we can say that for some circumstances they are not obsolete and in fact can be very useful.

Even a basic and cheap lead acid battery can supply a very large current which is required for car starting for example – some cars might need 600 amps or more to turn over especially if they are diesel or larger V8 and high compression engines.

They are also useful where there is no requirement for moving them as they weigh a lot for the usable power they contain. They are therefore no use for electric cars and for boats are very quickly self limiting especially if they need removal for charging asthey are very unwieldy.

The up front purchase price of lead acid batteries is generally much lower than lithium batteries making them cheaper to buy initially. However the number of cycles (times they can be used) that lead acid battery can last is generally very low especially when signficantly discharging them as we do in the marine environment so you will need to replace lead acid batteries far more often.

So Why Choose Our Lithium Batteries Over Lead Acid Batteries?

  • Lead acid batteries don’t suit situations where there is a lower power requirement for a longer period as they cannot sustain a deep discharge especially repeatedly. Lithium batteries can sustain much deeper discharge (generally 95% to 100%) with no long term damage.
    • This means our 100Ah lithium batteries are roughly equivalent to a 200Ah Lead acid battery for the usable power that you can access time and time again
  • The number of usable cycles on a lead acid battery where the reasonably deep discharge is required can be as low as a couple of dozen times to a couple of hundred maximum before the battery requires replacement
    • Our Lithium Iron Phosphate batteries are rated for 4000+ deep discharges by which time they will still supply 80% of their original capacity.
    • This means if you use the batteries twice a week a lead acid battery might last 2 years while the lithium battery will still be going strong fifteen or even twenty years later
  • Lithium batteries are much lighter than lead acid for a given amount of usable power eg our 12v 100 amp hour batteries weigh around 8.5kg while a normal lead acid battery will weigh around 25kg. Combine this with the safe depth of discharge (almost double that of the lead acid batteries) for our lithium batteries and you see the gains are immense!
    • The ease of getting the batteries on and off your boat is a key consideration
      • Hefting 25kg lead acid batteries around with unconfortable handles is no mean feat!
      • Alternatively, taking our batteries on and off your boat at a third of the weight for twice the power is very easy
  • The charging time for lead acid batteries is far longer than for the same amount of power for lithium batteries, meaning you can get your battery functional again far quicker
  • Connectivity options on the average lead acid battery are very limited to the large +ve and -ve terminals. You can buy multi terminal adapters allowing you connect other items but they are a bit clunky
    • Our Electric Outboard batteries all come with a variety of connectors such as Anderson plugs, 8mm ring terminal connectors, multiple how power USB connectors and voltage stabilised connectors for depth sounders. Simple plug and play – charge your phone or tablet, run your depth sounder and your electric outboard all at the same time as standard!
  • Most importantly all of our Electric Outboard own brand batteries use the Lithium Iron Phosphate chemistry not Lithium Ion technology making them far, far safer as they cannot overheat if there are any problems.
    • Shorting out or puncturing the batteries will not cause any of the potential issues seen with Tesla cars for example which use Lithium Ion technology


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