Battery charging issues: Common mistakes made by drivers
Those with a special understanding of batteries might think the question of how long to charge a battery seems simple. Undoubtedly, charging should continue until the battery is fully charged. However, many people are unsure about how long this process takes, and when to disconnect the battery charging device, such as a rectifier or charger.
4:39 PM EST, December 11, 2023
Often, drivers believe that batteries will charge overnight or within a day. Unfortunately, this assumption is wrong. A battery that is not fully charged performs less efficiently and has a shorter lifespan. It will also discharge faster, possibly causing issues when starting the vehicle.
The time required to fully charge a battery depends on several factors. Here, the battery's capacity and the charging current play a significant role. Furthermore, the source of charging energy also matters. Many charging devices like rectifiers and chargers exist in the market, with most operating in automatic mode. Note that a fully automatic charger turns off by itself once the battery is fully charged, though this isn't the case with rectifiers.
How to determine when a battery is fully charged
If you are using an electronic charger, it will either turn off once the battery is fully charged or an indicator will signal that the charging process is complete. If you are using a rectifier, the situation is a bit more complex.
As per physics, a battery can be considered charged when the electrolyte density reaches a certain value, depending on the temperature. For instance, at 68 to 77 degrees Fahrenheit, the electrolyte density should be about 0.048 ounces/in3. To confirm this, access to the battery's electrolyte is required to take a sample, and then density is measured using an areometer.
Another simpler method is to check the voltage at the battery poles using a multimeter, making sure to disconnect the rectifier or charger first. A fully charged battery's voltage is typically 12.8-12.9 V. For an accurate measurement, it's important to have a freshly charged battery in the multimeter (preferably not older than one year). Do note that depending on the multimeter's quality, the reading could vary. Thus, a battery indicating 12.7V can also be deemed as fully charged.
As you can see, the charge status of a battery isn't just a matter of time. Time isn't the deciding factor here, as the charging duration depends on the battery's capacity and the required charging current. Automatic chargers and rectifiers adjust the current value based on the battery's charge level over time. Therefore, it's impossible to calculate charging time even when aware of the standard charging current.
Lastly, different batteries require different voltages and charging devices. For instance, an AGM battery should only be charged with an electronic charger, with a maximum voltage of 14.9 V. A gel battery should only be charged using an electronic charger too, but with a maximum voltage of 14.4 V. Conversely, a battery with liquid electrolyte can be charged with a rectifier or charger, requiring a maximum voltage of 16.25 V.
