So you charge your battery up, but before you know it the unit is flat again. Its a common scenario, but the causes are varied. In this article we’ll go through what can cause the issue and how to fix it.
Parasitic electrical drains
One of the most frequent reasons batteries run flat quickly is that there is some drain occurring which is not immediately obvious. A well known one in vehicles is the faulty interior light which does not switch off when the door is closed. Unnoticed it gradually draws energy making the battery look like the guilty party when it is anything but.
Certain apps on laptops and smartphones can keep features running even when the device is left on standby. A worn out button on a remote control can get stuck down. The list of possibilities is long, but before beginning the hunt check that this is actually the cause.
First try fully charging the battery, removing it from the device and then testing it after whatever time period it usually runs flat. If the battery remains fully operational it is a parasitic electrical drain somewhere that needs to be rooted out. In larger appliances a multi-meter can help you track down the circuit which is drawing power from the battery. In laptops and similar devices try removing or disabling all the apps and then re-enabling them one by one until the fault re-occurs.
Is it actually charging?
Connecting your battery to a charger doesn’t mean it is charging. Some electrical devices such as smartphones and laptops have on screen indicators that confirm the battery is receiving a charge but many household and power tool batteries and those in vehicles are charged in isolation with only a possible indicator light on the charger to confirm charging is taking place or complete.
You can check chargers where the battery terminals are exposed during charging by connecting a voltmeter between the two. When charging the voltage should be slightly greater than the stated voltage of the battery. However for chargers which hide the terminals (such as those for cameras and power tools) the only way to confirm the charger is working correctly is to try a second one.
If you find that it is your charger that is faulty you might be able to find a replacement in our selection of battery chargers.
In vehicles specifically, a battery might not have time recharge after starting the engine if you make regular short trips or have an excessive number of electrical devices such as large sound systems operating. Here it will seem like the battery isn’t holding its charge, but in reality it is never really being fully recharged and you will need to plug it in to a wall charger from time to time to get it back up to a full state of charge.
Acid stratification in lead acid batteries
Lead acid vehicle batteries that are never fully recharged can also suffer from acid stratification. This is where the acidic part of the electrolyte becomes concentrated at the bottom of the battery which causes two issues. Firstly it means there is less acid in direct contact with the plates which makes it less effective in doing its job and secondly the more watery electrolyte at the top promotes corrosion of the plates reducing their future abilities even if the battery is fully recharged.
Acid stratification is worth a particular mention because when it occurs a battery can often have the same voltage as a fully charged battery giving the appearance that it is fully charged when it is anything but. This voltage issue can also lead some chargers to believe the unit requires no charge and so they will not operate.
The wrong charger
Different battery types charge in different ways and so need specific chargers. Most chargers pass a current through a battery until the battery reports a certain voltage has been achieved, but lithium-ion units are a good example of an exception to this rule – their voltage is fairly constant except when the battery is in a very low state of charge. As such a lithium-ion charger must monitor current and voltage and change the charge at various points. Trying to charge a lithium-ion battery with a charger for a different chemistry type can result in the charger reporting it has done its job when the battery is still close to empty, not to mention possible damage to the battery from passing the wrong current through it.
Changes in operating temperature
Batteries don’t like the cold, it reduces the amount of power they can deliver. This is why a car battery will work on a balmy autumn day, but fail the next morning when the weather has turned frosty. It is why you can jump start a vehicle and drive round town all day (stopping and starting with no issues as the engine has warmed up and so needs less power to start each time), but find the battery once again needs a jump start the next day.
All batteries – smart phone, laptop, power sports, two way radio and power tool batteries included – have the same issue. They run flat faster in the cold, not because they can’t hold their charge, but because the chemical reaction inside the battery is less efficient at lower temperatures reducing the time they can operate a device.
A badly constructed battery bank
Any device which needs two or more batteries to operate is being powered by a battery bank. Mixing amp hour (or milli amp hour) and/or voltages in a battery bank without the correct charging and discharging circuitry can cause damage to the batteries that will cause them to run flat faster than they should.
This issue is not limited to the electronic enthusiast building complex power sources. Batteries that have been charged and discharged a number of times have different capacities to new units with identical ratings, even when they are from the same manufacturer and brand so mixing new and old can reduce the ability of the battery bank to hold its charge.
Batteries from different manufacturers, but rated the same are never actually identical causing the same issue. As such it is always recommended that when a device has more than one battery they are all replaced at the same time with batteries of the same capacity from the same manufacturer, ideally produced at the same time.
For more detail on battery bank issues see Connecting batteries in series and Connecting batteries in parallel.
The battery has reached the end of its life
While there are numerous reasons why rechargeable batteries might not be holding their charge, the bottom line is they don’t last forever, even in ideal environments. With every charge and discharge internal chemical build ups reduce their ability to charge making their discharge times shorter and shorter. Batteries left for in a very low state of charge for long periods of time can also experience the same changes, so although they can report being ‘charged’, the active materials inside and available to power devices are limited. (see Why do rechargeable batteries die for a full explanation on this process).
At this point there is no option but to replace the unit.
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