Disconnecting, Removing & Replacing a Vehicle Battery:

It’s a fairly straightforward task to disconnect, remove & replace a battery in a vehicle. Often, all you need to do the job, is a socket and maybe a spanner (or a screwdriver). Sometimes, there are plastic covers or shroud’s over the top of the battery, that may need removing first. When disconnecting, there are a few things to watch out for…


Disconnecting the Battery:

To disconnect a vehicle battery, it’s always best to remove the negative terminal first.

Why should you do this?

The negative (‘-‘ ve) battery connection usually connects straight to the vehicle bodywork. If you disconnect the positive (‘+’ ve) connection first, you could accidently touch an uninsulated part of the bodywork, or engine at the same time, (with your hands, or something that conducts electricity like a spanner). This could result in an electric shock, or there could be lots of sparks, (see the safety precautions below)!

Safety Precautions:

  • Do not short the battery connections, (or yourself across the battery, it could give you a shock!). 12 volts is not usually enough to kill you, but batteries larger than 12v may do?
  • Lead acid batteries produce Hydrogen gas. If enough gas is produced, the battery can ignite from a spark, causing an explosion. One of the products of a battery explosion is acid burns…


  • A negative battery terminal will often be marked with a (‘-‘ ve) symbol.
  • The vehicle bodywork often acts as a return path (a wire) back to the battery, (if it’s a fiberglass vehicle a negative cable has to be run back to the battery).
  • As well as being a negative (‘-‘ ve) connection, anything connected to a vehicle’s bodywork is often called an ‘earth’. Earth and negative can be very confusing terms on vehicles, (as you would never connect a negative lead to earth on household electrics as this would cause the circuit breaker to trip, or the fuse would blow).

Connecting the Battery:

When reconnecting the battery, it’s best to connect the positive (‘+’ ve) battery terminal first.


The negative connection from the battery usually connects straight to the vehicle bodywork. If the negative (‘-‘ ve) is connected first and you then connect the positive terminal (whilst you are touching an uninsulated part of the bodywork or engine), you could get a shock, or sparks, (see the Safety Precautions: above)!

Things to Watch out for (What can go Wrong)?

Is There a Radio Code?

The vehicle handbook advised that a radio security code would be required if the battery was disconnected. However, when the battery was reconnected (after 4 hours), the radio unit worked straight away without needing a code?

Were the Windows Open When the Battery was Disconnected?

The handbook advised that a reset of the electric windows may be required on disconnecting the battery? I kept all the windows shut, so I didn’t need to reset… The handbook did advise how to reset the window operation, so have a look to see if there is one for your vehicle, (or make sure the windows are shut)?

Dashboard Warning Lights?

The handbook gave no advice on issues with the dashboard warning lights on disconnecting the battery. However, on putting on the ignition, I had the tyre (tire) pressure, stability control and the steering wheel warning lights come on? When starting the engine and remaining stationary, they didn’t disappear?

So, I took the vehicle for a short drive and within 100 yards the warning lights cleared.

Don’t Leave Your Keys Inside the Vehicle!

To be on the safe side, never leave your keys inside the vehicle… Just in case the vehicle decides to lock itself after reconnecting the battery?


Even when the battery hasn’t been disconnected, some vehicles will automatically lock themselves if left unattended for a short period of time. So it’s always best never to leave your keys inside the vehicle, just in case…

Other Things to be Aware of?

Warning – If you’re disconnecting the battery to work on the vehicle, beware of reconnecting the battery before all electrical connections have been reconnected.

I disconnected the battery to remove an entertainment head unit, (radio, media player, etc) which also contained an air bag warning light. I reconnected the battery to test the entertainment head unit, before reconnecting the air bag warning light. This latched an air bag warning light on the dashboard, which didn’t clear itself after reinstalling and reconnecting everything back into the vehicle…

To reset and clear the air bag warning light, required connecting the vehicle to a device that would clear the vehicles internal fault memory. If you don’t have such a device, it’s a trip to a dealership, or your local garage.

Hope this info helps… 😄👍

Exit mobile version