How to charge a car battery

How to charging a car battery.  They go flat for lots of reasons, here are a few ;

* Battery getting old
* Car has been standing for a while
* Alternator not charging
* Lights have been left on
* Very cold weather

Car battery chargers ;
* Are really easy to use
* Are cheap
* Save you lots of hassle
* Save you money (on new batteries)

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How to charge a car battery
This is a typical car battery charger


* Battery charger,
* Spanner (usually 10mm or an Adjustable),
* Up to 8 hours charge time (overnight),
* Possibly some distilled or de-ionised water.

If your car is parked close enough to your house or in a garage, then you can leave the car on the battery whilst it is charging.  However, you must disconnect both red and black battery terminals (probably with your 10mm spanner) ;

Removing a Car Battery
How to Remove a Car Battery from your Vehicle

If it is not, then you will have to take the battery off the car, so watch the video below to see how easy it is.


Once you have taken off the battery, take it to a safe area with plenty of ventilation and away from kids, pets, naked flames and sparks.

Check the labels on the battery to see if you need to remove any of the ‘cell caps’ whilst charging the battery.

Some batteries are sealed units and do not have these, but if yours has ‘cell caps’ they will be situated on the top, they are normally under a press-on strip, others will be circular caps for individual opening (see pics below).

car battery charging

car battery top

This battery has caps under the yellow  strip

This battery has the individual caps

car battery cell caps removed
This battery has had the cell caps removed.

Either remove the press-on strip or individual round caps before connecting the battery charger.  This will allow any gases created during charging to escape and not build up inside the battery – this is why you need to put the battery in a well ventilated area.

car battery on charge
Typical car battery being charged.


BEFORE YOU CONNECT – Before you connect the battery charger, you will need to check the levels inside the battery – this is very easy.  If they are low, then you need to top up the cells with ‘distilled’ or ‘de-ionised’ water, this is the stuff you are supposed to use in your iron, so it is available from the supermarket in the laundry section.  My recent bottle cost 60p. DO NOT USE TAP WATER, under any circumstances do not use tap water, it will damage the cells inside the battery and you will have to buy a new battery.

I recently had to top up my car battery with distilled water before I charged it up. It only cost me 80p for a bottle, and I got it from my local corner hardware shop.  That 80p saved me the cost of a new battery.

It is important to ensure that the metal plates / cells inside the battery are covered with electrolyte. DON’T PANIC, electrolyte is just the mixture of acid and distilled water inside the battery and if the cells are not covered by the electrolyte liquid they will get damaged and you will need a new battery.

inside car batterycar battery electrolyte
Here are a couple of drawings showing the inside of the battery and the cells / plates that need to be covered by the electrolyte.

How to charge a car battery
Checking inside car battery cells

All you need to do once you have removed the cell caps is have a look down inside all of them (ideally use a small torch) ;

Looking into the cells, you can see they have
been filled so that the plates are covered with the electrolyte.

Most batteries have a minimum fill level when you look inside them, so topping up is very easy and very cheap.  DO NOT ignore the importance of topping up your car battery, it can save you ALOT OF MONEY.

If you are leaving the battery on the car then disconnect the negative (black) and positive (red) wires from the battery using the relevant spanner (usually 10mm).

Before you go any further, make sure you have read the manufacturers instructions that come with the battery charger.

With the battery charger unplugged from the electricity supply, connect the black charger clip to the negative ( – ) terminal of the battery and the red clip to the positive ( + ) terminal.

Now plug the car battery charger into the mains and switch it on.

Leave the battery charging overnight and when you check on it in the morning the charger should indicate that the battery is fully charged.

Switch off and then unplug the charger, remove the charger clips from the battery and refit the cell caps / strip.

The battery should now be ready to refit to the car, follow the removal instructions in reverse.

THEN, start your car – AND OFF YOU GO

and you will also be bending over, so if you have back trouble, be more careful and perhaps get someone to help you with the lifting.

Topping up your battery with distilled water – Some battery chargers will show when the battery is full. But if you know the battery to be flat but the battery charger is showing it to be full.  Make absolutely sure that the battery is topped up enough.  (I recently had to charge a car battery and thought I had put enough distilled water in it but when I connected the charger, it said that it was fully charged.  So I added some more distilled water to all of the cells and then the FULL LED on the charger went out and the charger started doing its work). If the battery is correctly filled and the charger is still saying full, chances are that the cells in the battery are damaged and you will need a new car battery.

If your car battery keeps going flat, then there is something wrong, possibly with the battery or the alternator or something else. Check out the rest of our HOW TO articles to test other parts.

NOTE – make sure you always read the manufacturers instructions for all equipment and appliances.

If this was article useful, subscribe to our also useful Newsletter, you can read more about it here – CarBasics Newsletter

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