Why won’t my battery charge?

So you connect your battery to a charger and after a few hours nothing has changed. A common issue, but one with many causes.

Some basic checks

Is the charger getting power? It might sound obvious, but it could be that the plug socket is at fault, not the charger. Most chargers have an indicator light which confirms that all wiring is connected correctly and drawing power, but some don’t. If yours doesn’t, try a different socket. If the battery is in a vehicle where it is meant to be charged by an alternator, check that the alternator is operating.

Is the charger working? If the battery is in a vehicle where it is meant to be charged by an alternator, check the alternator is operating by using a voltmeter to test the cross circuit voltage of the battery.

Chargers with an indicator light confirming the charger is plugged in to a working socket do not always mean it is working correctly.

  1. Try using an identical but different charger
  2. Try charging a different battery (if you have one that the charger is designed for)

If you conclude your charger no longer works you might find a replacement in our selection of battery chargers.

Are you using the device while it is charging? In vehicles the battery can use a great deal of its power to get the engine started and it will take time to recharge. In cold weather a newly started car will be trying to recharge the battery while powering items such as headlights, fans, windscreen wipers, window defrosters, etc. A short journey to the local grocery and back again won’t give it enough time to recharge the battery. If this is your driving pattern on a regular basis you will also need to charge the battery from time to time with a wall charger.

On some electrical devices such as smart phones and laptops it is also possible to be using intensive apps which take all the power the charger can provide. Switch the device off or close down all the apps and see if the battery starts to charge.

Check the battery temperature. Batteries don’t like the heat and it can affect their ability to charge. Mobile devices and laptops can get exceptionally hot inside, so try turning the unit off for several hours and then charging it.

Vehicles can also get extremely hot under the hood – either because of heat from the engine or when they are sitting in direct sunlight in warm climates such as the southern states. Try removing the battery and taking it to a cooler location such as an air conditioned room. Give the unit several hours to fully cool down and then see if it is better at taking a charge.

Is the battery actually connected to the charger? It sounds odd, but think again. On a vehicle battery with dirty terminals or a broken cable this might mean there is no connection between battery and charger. Use a voltmeter to see if the cross circuit voltage of the battery rises when you connect the charger.

On smaller devices this issue can be more difficult to check as the wiring is very small and can run through boards where circuits are so tiny they cannot be made out by the human eye. The only real way to test here is if you have another device that can use and charge the same battery to see if it will charge your unit.

Switch it off and on again. Yes, that enduring advice from most computer helplines isn’t just for computers and it might just work. The charging of some devices is controlled by coded programs and they can malfunction. A reset might help put them back on track.

Charging in modern vehicles is also computer controlled, but to achieve a reset here you’ll need a mechanic with the right hardware and software.

Check for physical damage. Check the battery itself for signs of cracks, corrosion, leaking or bulging. All of these will indicate mechanical failure and can occur even in a well cared for battery.

How did the battery fail?

With the basic checks out the way how the battery failed can provide clues as to why it won’t charge.

It charged fine yesterday, but it won’t charge today

If the battery is less than six months old this suggests a short circuit caused by a manufacturing defect. The battery should be replaced under warranty.

If the battery is several years old this suggests “old age”. With every discharge and recharge a battery looses some of its capacity due to chemical build up on the plates. Its possible that the battery has charged, but not to the level where it can power the device and it will not be able to reach this level again. Its time to get a replacement.

See also Why do rechargeable batteries die.

It hasn’t been used for several months

All rechargeable batteries are designed to charge and discharge on a regular basis. Left unused they slowly run flat and chemical reactions can occur which cause internal damage. In many starter batteries, for example, sulfates build up on the plate and crystallize which stops the unit from being able to charge.

These problems are extremely common in batteries that power seasonal devices such as lawn mowers and jet skis. They can be avoided by regular periodical charging or continuous connection to a smart charger which monitors the state of charge and turns on automatically when needed.

No battery likes to run completely flat. In some lead acid batteries this can cause the plates to buckle and shed the active paste they need to take a charge. The life of lithium-ion batteries is also dramatically shortened if it is left completely discharged.

Batteries will slowly discharge naturally even if not in use. Its also a common mistake to think batteries connected to a device which is not in use are not discharging. Vehicle batteries often continue to power on board computers and clocks whose trickle drain will completely exhaust the unit. Laptop or smart phone batteries can still be providing stand by applications.

Again periodical or smart charging can help avoid this, but if you haven’t used a battery for several months and now it won’t charge, the chances are it is completely dead and needs to be replaced.

See How to store batteries for more on the best way to keep a battery healthy when not in use.

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