A dire question has recently popped up from the battery-using community- whether they should use a lead-acid charger to charge LiFePO4 batteries, where the answer can be twofold.
In this article, we’ll discuss when you can use it and why you shouldn’t use it with LiFePO4 batteries.
Can I Charge LiFePO4 With A Lead Acid Charger?
You can use a lead acid charger to charge your LiFePO4 battery, provided it has the same voltage rating as your battery. But there are other factors like float charging, equalization mode, etc., charging parameters why experts recommend using lithium iron phosphate charger.
Let me first discuss when you can use a lead acid charger with a LiFePO4 battery. When the charger’s voltage parameter matches your LiFePO4 battery voltage requirement, you can only use them together.
Again, the LiFePO4 battery doesn’t need float charging, a requirement for SLA batteries. That’s why SLA chargers come with a float charging option. But when you use an SLA charger to charge your LiFePO4 battery, you must switch off the float charging option.
LiFePO4 batteries have two charging stages. They do not require float charging. If you cannot switch off the float charging option, it will overcharge your LiFePO4 battery. You should also turn off the equalization option from your lead-acid charger.
Failing to ensure those can be detrimental to your battery. LiFePO4 is a pure battery that only consumes what it can absorb. On top of that, the lead acid charger cannot revive a sleeping or disconnected LiFePO4 battery. Only a lithium iron phosphate battery can do that.
Why Shouldn’t You Charge LiFePO4 With A Lead-Acid Battery?
Voltage is the main reason you shouldn’t charge the LiFePO4 battery with a lead acid charger. A 12V LiFePO4 battery voltage remains around 13.3 to 13.4 volts at 100% state of charge. A lead acid battery voltage remains between 12.6 to 12.7 volts.
The following table shows the voltage of various LiFePO4 batteries at 100% state of charge.
| Nominal Voltage | At 100% State of Charge |
| 3.2V | 3.4V |
| 12V | 13.5V |
| 24V | 27V |
| 48V | 54V |
So, lead acid batteries are designed to charge lower voltage SLA batteries, which can be a problem when using this charger with a LiFePO4 battery. Lead acid batteries charge at a lower voltage compared to LiFePO4 batteries’ requirements.
According to a study published in ScienceDirect, lithium iron phosphate batteries are voltage-limiting devices that have some similarities with lead acid charger systems. But LiFePO4 chargers have higher voltage in each cell than lead acid. Besides, they have more voltage tolerance and no trickle or float charging option.
Lead acid batteries and chargers are a bit flexible regarding voltage and overcharging. But LiFePO4 batteries are very strict on balance and do not accept overcharging. That’s why you shouldn’t charge your LiFePO4 battery with an SLA charger.
It will charge slower and won’t charge your battery to full capacity. Besides, lead acid chargers with a lower amperage rating are incompatible with a LiFePO4 battery. So, it’s recommended not to charge LiFePO4 batteries with a lead acid charger.
Is Lead Acid Charger Algorithm Suitable For Lifeopo4 Battery?
Most lead acid batteries now have specific algorithms suitable for AGM/Gel batteries that fully charge with 3 stages. This charger will maintain maximum voltage at a reduced current as the internal resistance won’t accept the highest current output.
The lead-acid charger will enter the float stage when the current is reduced to less than 10% of your charger’s total output. But a LiFePO4 charger has only two stages, and it has a steep rise in voltage at the end of the charging cycle.
The charge current will drop fast, and the LiFePO4 charger will switch to power supply mode. As you can see, there are some differences between the lead-acid and LiFePO4 charger algorithms.
Final Thoughts
While you can charge your LiFePO4 battery with a lead-acid charger, it’s not highly recommended. It can reduce your battery capacity and create damage in the long run.
By the way, If you wondering to find another alternative way to charge your LiFePO4, the external power source could be a help for you too.
References
1. Y. Hu et al. (2011). Charging Method Research for Lithium Iron Phosphate Battery.
Eng. Matthew Joseph Nandirio is the Founder of walkingsolar.
After graduating from the University of Houston in 2002, matt started working as a Solar Electrical Engineer for several multi-national solar energy companies.
He has a wide range of experiences including solar system requirement analysis, planning, maintaining, debugging and even solar device development through research.
He now shares his 20 years of expertise through his articles on the walkingsolar website.
Further, he is also the author of two books on Solar Technology, “Solar Power for Villages” and “DIY Solar System for Dummies”.