Overview
“Can LiFePO4 battery cells be charged with a Lead Acid charger?” This is the question we recently get from our customers.
Please find below the answers to why it shouldn’t be done. Simple answer: it is not recommended, because you have to be VERY CAREFUL and you SHORT your battery life.
Charging Conditions
Much like your cell phone, you can charge your LifePO4 batteries whenever you want. If you let them drain completely, you won’t be able to use them until they get some charge. Unlike lead-acid batteries, LifePO4 batteries do not get damaged if they are left in a partial state of charge, so you don’t have to stress about getting them charged immediately after use. They also don’t have a memory effect, so you don’t have to drain them completely
when charging
LifePO4 batteries can safely charge at temperatures between -4°F – 131°F (0°C – 55°C) – but we recommend charging in temperatures above 32°F (0°C). If you charge below-freezing temperatures, you must make sure the charge current is 5-10% of the capacity of the battery.
What About During Storage?
LifePO4 batteries are easier to store than lead-acid batteries. For short-term storage of 3-6 months, you don’t need to do everything. Ideally, leave them at around 50% state of charge before storing. If for long-term storage, it is better to store them at a 50% state of charge and then cycle them by discharging them, recharging them and then partially discharging them to approximately 50%, every 5-12 months.
The Key Differences between LifePO4 Battery cells and Lead-Acid Batteries When Charging
LifePO4 battery cells can charge at a much higher current and they charge more efficiently than lead-acid, that’s meaning they can be charged quickly. LifePO4 batteries do not need to be charged if they are partially discharged. Unlike lead-acid batteries, which when left in a partial state of charge will sulfate, drastically reducing their performance and lifespan.
A 12v LiFePO4 battery cell fully charged to 100% will hold a voltage of around 13.3-13.4v. Its lead-acid cousin will be about 12.6-12.7v. A LifePO4 battery cell at 20% capacity will hold a voltage of around 13V, its lead acid cousin will be about 11.8v at the same capacity.
A LiFePO4 charger is a voltage-limiting device that has similarities to the lead acid system. The differences with LifePO4 lie in a higher voltage per cell, tighter voltage tolerances, and the absence of trickle or float charge at full charge. Even if lead acid offers some flexibility in terms of voltage cut-off, manufacturers of LifePO4 cells are very strict on the correct setting because LifePO4 cannot allow overcharge. The so-called miracle charger that promises to prolong battery life and gain extra capacity with pulses and other gimmicks does not exist. LifePO4 is a “clean” system and only takes what it can absorb.
LifePO4 chargers are based on a CV/CC (constant voltage/constant current) charge algorithm. The charger limits the amount of current to a pre-set level until the battery reaches a pre-set voltage level. The current then reduces as the battery becomes fully charged. This system allows fast charging without the risk of over-charging and is suitable for LifePO4 and other battery types.
LifePO4 Battery Charger Algorithm Example
The LifePO4 battery cells have a steep rise in voltage at the very end of the charge cycle. At this stage, the charge current drops extremely quickly and the charger then switches to power supply mode.
The majority of the lead acid smart chargers these days have specific charge algorithms to suit Flooded/AGM/Gel batteries which generally require a 3-stage charge process, Bulk/Absorption/Float. Once the charger enters the bulk state, it will normally charge a lead acid battery at full current to approx 80% capacity. At this point, the charger will transition to the Absorption stage. Connecting LifePO4 batteries in series is much like connecting them in parallel, it is best to charge each battery up individually and check the voltage and ensure they are within 50mV (0.05V) of each other before making the series connections.
It is highly recommended to charge 12v LifePO4 batteries in series with a multi-bank charger. This means each battery is charged at the same time but completely independent of the other.
Lead Acid Charger Algorithm
1. BULK
Charges the battery using the maximum current until the absorption voltage is reached. At the end of the bulk phase, the battery will be about 80% charged and ready for use.
2. ABS – Absorption
Charges the battery using a constant voltage and a decreasing current until it is fully charged. See the above table for the absorption voltage at room temperature.
Variable absorption time:
The absorption time is short (at least 30 minutes) if an almost fully charged battery is connected and increases to 8 hours for a totally discharged battery.
3. RECONDITION
RECONDITION is an option for the NORMAL and HIGH charging programs and can be selected by pressing the MODE button again after selecting the desired charging algorithm.
During RECONDITION, the battery is charged to a higher voltage using a low current (8% of the rated current). RECONDITION takes place at the end of the absorption phase and ends after one hour or sooner once the higher voltage has been reached.
The RECONDITION LED will be lit while charging and will blink during RECONDITION.
Example:
For a 12/30 battery charger: the reconditioning current is 30 x 0.08 = 2.4A
4. FLOAT
Float charging. Keeps the battery at a constant voltage and fully charged.
5. STORAGE
Storage mode. Keeps the battery at a lower constant voltage to limit gas formation and corrosion of the positive plates.
6. READY (battery fully charged)
The battery is fully charged when the FLOAT or STORAGE LED is lit.
7. REFRESH
Slow self-discharging is prevented by automatically ‘refreshing’ the battery with a brief absorption charge. Some lead acid chargers “ping” the battery on startup to determine the voltage/resistance of the battery. Based on return information, the charger then determines what charge phase to start in. Because LifePO4 battery cells will hold voltage above 13+v, some lead acid chargers will see this as a nearly full battery and enter into a floating stage and bypass the charge stage altogether.
Conclusion:
If you want to use a lead-acid charger on a LifePO4 battery cell you can, HOWEVER, you must NOT use a lead-acid charger if it has an automatic “equalization mode”, which cannot be permanently turned off. A lead-acid charger that can be set to charge no higher than 14.6v can be used for regular charging and then MUST be disconnected after the battery is fully charged. DO NOT leave the lead-acid charger connected to maintain or store the battery, because most will NOT maintain the proper voltage charge algorithm for LifePO4 battery cells and damage will occur to the battery and this is not covered under the battery warranty.
