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What Happens to the Battery with Reverse Polarity Wiring Connection

Charging & Discharging the Battery with  Incorrect and Wrong Connection

We know that a secondary battery (also known as an accumulator) is a device that converts the chemical energy into electrical energy and stores in it for later usage. The chemical reactions in secondary cells are reversible in case of proper battery polarity connection instead of reverse polarity.

In other words, the chemical components in the battery can be reversed (to the original and prior shape) by changing the direction of flow of current in the battery. The flow of current in discharging mode (battery supply power to the connected devices) is opposite in case of charging (external source provides energy to) the storage battery.

There are internal plates in the batteries (lead acid, alkaline etc) known as cathode (positive “+”) and anode (negative “-“). For example, the positive plate is Lead per oxide (PbO2) and the negative plate is sponge lead (Pb). A light sulfuric acid (H2SO4) is used as an electrolytic solution in the battery for proper chemical reaction.

The combined chemical reaction in the battery can be written as follows during the charging and discharging (or discharged and charged cell) of lead acid battery:

    Positive Plate               Negative Plate                  Electrolyte              Discharge            Positive Plate                   Negative  Plate             Water

PbO2        +        Pb        +        2H2SO4            ⇋             PbSO4       +         PbSO4    +   2H2O


  • PbO2  +  Pb  +  2H2SO4 = Cell Charged
  • PbSO+  PbSO+  2H2O = Cell Discharged
  • Whole Equation (Left to Right) = Discharge i.e. discharging action
  • Whole Equation (Right to Left) = Charge i.e. charging action

When using a battery for both charging and discharging, it is necessary to connect the positive terminal of source to the positive terminal of battery and negative source to the negative terminal of battery. OK got it, but what happens if you put batteries the wrong way? OK, let’s know about the polarity and reverse polarity in the batteries.

What Happens to the Battery with Reverse Polarity Wiring Connection

What is Polarity & Reverse Polarity in a Battery?

Battery Polarity

Polarity means having opposite physical properties at different points. In case of battery, the one pole or plate having more electrons is known as anode or negative (-) terminal. The other having less number of electrons is known as cathode or positive (+) terminal.

If we connect these both terminals through a conductor having a resistance, the current will start to flow due to the potential difference on both points. In other words, the electrons (electronic current will start to flow from the -Ve terminal to the +Ve terminal. The electrical (conventional) current flows in the opposite direction i.e. from positive electrode the negative electrode.

Battery Reverse Polarity

Battery reverse polarity is the case when the source (for charging) or load cables are connected incorrectly i.e. source or load Negative to the Positive of battery and source or load Positive to the Negative terminal of the battery. Due to the wrong connection, a current may start to flow in the circuit and may cause some serious injuries and damage to the equipment.

Enough the basic, now come to the point i.e. what happens to a battery if you recharge it the wrong way around? or what happens when charging a battery using reverse polarity with a charger?

There are three scenarios as follows

  • Connecting a battery to the charger with reverse polarity
  • Connecting Battery to the load with reverse polarity
  • Connecting a battery to another battery with reverse polarity

Let’s discuss one by one in detail.

Connecting a Battery to the Charger with Reverse Polarity

If by chance, accidentally or intentionally the battery charger (or solar panel, Inverter etc) connected to the wrong way around i.e. the charger negative and positive connected to the battery positive and negative terminals respectively, the following may occurs:

  • The current flowing to the battery through the charger may burn out the electronic components inside the charger (if there is no reverse protection is provided by the manufacturer). In short, It may partially or fully damage the charger circuit. If the rating of charger is less than the battery capacity, it would overload the circuit and may turn off the circuit breaker to terminate the circuit operation. If the rating of charger is greater than the battery capacity, it may overheat the battery and burn with expulsion.
  • It may discharge the battery with spark or permanently damage the battery. In other words, the reverse polarity battery connection, the DC supply would drag electrons from the negative terminal of the battery and push them at the positive terminal. This would gradually discharge the battery same like in case of a capacitor.
  • The heat produced by the reverse polarity in the battery may cause hydrogen gas (ignitable) which may explode the battery casing. The cracked case of the battery may provide a way for acid which may melt the sensitive devices and cause serious injuries as well.

For these reasons, wear rubber gloves and glasses for proper protection while working on batteries.

In addition, there is an exceptional case as well where a battery may be connected to the incorrect way.

The battery can be connected to the wrong terminals when it has been fully discharged. As the fully discharged battery having 0 volt potential difference acts like an empty vessel (dead battery). In this case, the battery positive terminal can be connected to the negative source terminal and the battery negative terminal can be connected to the positive source terminal. 

This is not always the case and wont work for all batteries due to the different pastes/materials and technique used in the batteries. While in old batteries, it may work for years but some of tested experiments reported the less efficiency & capacity, quick drainage and short life of battery. The battery charged with reverse polarity should be marked interchangeably i.e. the battery (+) should be marked as (-) and vice versa. To reverse the action as prior, fully discharge the (reversed charged) battery and connect it to the right terminals (i.e. negative to the negative and positive to the positive terminals of charger and battery respectively).

Again, wear the rubber gloves and glasses and other safety measures for proper protection while playing with batteries.

Connecting Battery to the Load with Reverse Polarity

The same case i.e. battery connected to the wrong way but load appliances instead of charger. This may lead to the following phenomena:

  • Some load may not work properly (i.e. LED or Diodes) which works only in a single direction or it needs a proper DC supply connection to be fully functional as anode (-) to anode (-) and cathode (+) to the cathode (+) terminals).
  • In case of vehicles and automobiles, the car battery with reverse polarity may damage the ECU (Engine Control Unit (electronic control board), in automatic vehicles) electronic sensors and Alternator which are little bit expensive to replace with new ones.
  • It may also damage the other components and vehicle wiring systems. If you are lucky by luck, at least the fuses and relays may blow at all due to the reverse current formation.
  • The DC clock and analog motors as load connected to the battery may start to rotate in the backward direction.

Nowadays, the modern vehicle manufactures put a reverse polarity protection in the system as it is easy to manage it instead of the useless and number of support calls and maintenance. But is it OK and satisfied to give it a try? Not at all.

In addition, a fuse or a generic diode (Voltage drop up to 0.7V across the diode will occur) can be installed on the positive wire for one direction power supply which acts a reverse current protection.

Connecting a Battery to Another Battery with Reverse Polarity

If a battery in the first car is connected wrongly to the battery placed in another car to charge the second battery through the first one, it may explode and burn or permanently damage the battery(ies). The common batteries as lead acid may heat up and melt the internal and external parts in the battery. The ignite gas as hydrogen may crack the battery casing with exploration. 

In case of a wrong connection of batteries instead of proper series connection, both the batteries will oppose each other hence the result will be equalized charged on both i.e. they will quickly flatten each other.

It may also melt the jumper cable and insulation connected between the two batteries as it is not designed or rated for a huge amount of electric current due to the incorrect connection.

Safety Precautions:

  • Please wear safety glass and rubber gloves and other safety measures while working around the batteries and related hazardous equipment.
  • Use the proper wiring color codes according to your regional codes for batteries connections.
  • The author will not be liable for any losses, injuries, or damages from the display or use of this information or if you try any circuit in wrong format. So please! Be careful because it’s all about electricity and electricity is too dangerous.

Now its your turn, please express your feeling and real time experience with the batteries reverse polarity connection in any aspect. We really want to know your taught on this topic.

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  1. Your anode and cathode polarity information is not correct. Anode is usually positive side and the cathode is negetive side while you has written it completly opposite in upper paragraph. So i suggest you to correct this mistake??

        1. Anode and cathode are defined by the oxidation and reduction processes taking place in the batteries (galvanic & electrolytic cells) Please read more about the oxidation process to clear the basic concept.
          For example; Oxidation occurs in anode. Loss of electron is oxidation. Only negative can lose electron.So anode is negative and vice versa.
          In addition, the concept is little bit other than the galvanic and electrolytic cells in case of semi conductor devices such as Didoes e.g LED etc.
          The final read is (flow and direction of) conventional and electron current.

          1. Hi anode is positive and cathode is negative terminal please check it and do it correct in paragraph ?

  2. Is my brand new battery ruined if I merely touched the wrong terminals a couple times which caused my horn to blow. It also blew my fusible link and a few other fuses. Is the battery still ok? Or can I return it as a bad battery?

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