One of the most common causes of lithium battery failure or degradation is improper charging. While these power packs, especially the famous lithium iron phosphate battery, are significantly better than lead-acid batteries, charging a lithium battery incorrectly or with an inappropriate charging device can result in irreversible battery issues.
Let's start with a strong fact: Charging lithium battery with lead acid charger is not recommended. The voltage difference between the two battery chemistries is narrow but present, making their charging equipment unsuited for each other.
A fully charged 12V lithium battery will read around 13.4 - 13.5V. Its lead acid counterpart will have a voltage level of 12.6 - 12.7V at the same state of charge.
If you discharge your lithium battery down to 20%, it will hold a voltage of around 12.9V. At the same time, its lead acid cousin will have approximately 11.8V at the same capacity.
See that gap? That's the first reason why it's always best to use the appropriate charger for the type of power pack you have. If you want to know more about how to charge a lithium battery properly, keep reading!
LiFePO4 Battery Charging: Lithium vs Lead Acid Charger
Still not convinced? Check out this comparison between charging a LiFePO4 with the appropriate 12V lithium battery charger vs a lead-acid battery charger.
Voltage Limits
LiFePO4 battery chargers are typically voltage-limiting to help avoid overcharging. They tend to have stricter, more rigid settings to lessen the risks posed by excessive charges such as fires or battery explosions. Traditional lead acid chargers, meanwhile, offer more flexibility in terms of voltage cut-offs.
Modern lithium batteries used in some caravans and cars have expensive built-in electronics that can compensate for these charging differences, but you need to make sure this is present before using a lead-acid type charger to top off your lithium-based power pack. Still, it’s best to go for the correct type of charging equipment for utmost efficiency, safety, and convenience.
Charging Profile
Charging a lithium battery requires a slightly higher charge voltage and a deeper constant voltage at the end of the cycle, which helps get the power pack to a full 100% State of Charge (SOC). Lead-acid charging profiles normally cannot achieve this although they can get close, maybe around 95%.
The two batteries’ charge profiles also have different "return to boost" behaviour. In the case of lithium batteries, the charger monitors the voltage right after a complete charge cycle then decides when to switch back to boost/bulk charge mode and restart a full charge cycle again.
Lead acid batteries differ here because they wait for the voltage to drop extremely low before restarting the charge cycle. This is mainly because it has a lower resting voltage compared to a lithium battery.
Here’s a closer look at the difference between the two batteries’ charging profiles.
A lead acid battery is usually charged using a 3-stage method: Initial stage, saturation topping charge, and float charge.
The first stage serves to limit the current to avoid overcharging the battery. It's normal for the charging rate to fluctuate here, stabilising as you near the full charge voltage limit. The second stage starts upon reaching the voltage limit, wherein the current draw gradually decreases and terminates when it falls below 5% of the battery's rated capacity.
Last, the float charge phase is used when your battery is on standby to keep it at a 100% State of Charge (SOC). This helps prevent sulfation, one of the leading causes of battery damage.
Moving on to the LiFePO4 Battery charging profile requires only the first two stages. Still, the advantage here is that the charge rate is much higher, resulting in a faster charging time.
Stage 1 in lithium batteries usually occurs at 30%-100% current of the battery's rating. This can be completed in just an hour if you’re using the appropriate LiFePO4 battery charger, making your battery available for use in a short time. The second stage is also necessary to bring your power pack to 100% SOC. This can be done in as little as 15 minutes for a lithium-based battery. If you look at it overall, the total charging time of a lead-acid battery typically takes 10 hours. In comparison, that of a lithium battery takes only four hours!
The absence of stage 3 is normal for a lithium battery. In the case of long-term storage, a lithium power pack should not be stored at 100% SOC, meaning they can be maintained with a full cycle once every 6-12 months and stored at only 50% SOC.
What Is the Best Way To Charge A Lithium Battery?
So, how do you charge lithium batteries? The first thing you need to ensure is that you use the right lithium battery charger and set it within the appropriate voltage limits.
In terms of charging conditions, lithium power packs can safely charge in temperatures above 32 °F. If you need to top it off at freezing temperatures, see to it that the current is between 5-10% of the battery's capacity to prevent damage.
Charging Lithium Batteries in Parallel
Charge each battery individually before connecting them in parallel, checking the voltage and ensuring each one is within 50mV of the other before wiring them. This will help minimise the imbalance between batteries and keep their performance at maximum level.
Charging Lithium Batteries in Series
The same practice goes with connecting your power packs in series. For best results, you can use a multi-bank charger, which keeps each battery charged separately to maintain balance within the cells.
If you're using solar power to charge your battery, always use a solar charge controller (preferably an MPPT charge controller) between your battery bank and solar panels. This will regulate the energy your panels generate, which will be stored in your power pack.
Knowing how to charge a lithium battery is a crucial part of maintenance. These batteries do not come cheap. While they are known to be superior for overall quality, how you handle them while in use and after use plays a huge role in their performance and longevity.
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Last Updated on April 5, 2024
