What's the best off-grid battery options between Lead-Acid and Lithium Iron Battery?
As we all know, lead-acid batteries haven’t changed much in 100 years, and they have a long history of dependability and affordability. They’re typically named according to the electrode material used, and further defined by the electrolyte used.
Batteries are designed for specific purposes. Starting, lighting, and ignition (SLI) batteries used in cars are engineered to release lots of energy in a short period of time, and then quickly receive a recharge. Deep-cycle batteries have thicker plates, allowing for greater energy storage capacity and deeper discharging. The deep-cycle, flooded lead-acid (FLA) batteries are most likely lead-acid batteries to be used in off-grid applications.
Lithium-based batteries are engineered for performance and represent advanced energy storage. Several configurations are in use today, each with different electrode and electrolyte chemistry, charge and discharge characteristics, specific energy, costs, and safety factors. For this comparison with deep-cycle FLA batteries, I’ll focus on lithium iron phosphate batteries (LFP).
Breaking Down Batteries
Lithium iron phosphate (LiFePO4) technology is named after its cathode material. LFP batteries are gaining popularity for automotive, offshore, and off-grid use as a direct replacement for lead-acid batteries. For this comparison with deep-cycle FLA batteries, I’ll focus on lithium iron phosphate batteries (LFP).
Safety is a widely publicized concern with lithium batteries. Lithium-ion batteries are under internal pressure and contain a flammable electrolyte, so they need to be durably packaged, and handled and charged with extreme care. Lithium-ion is not the same as LFP batteries, LFP uses an inherently safer, more stable design based on different electrode alloys and electrolyte.
Battery lifetime is expressed as the number of charge and discharge cycles a battery can survive before losing a certain percentage of capacity. Deeper discharge results in fewer total cycles and overall reduced lifetime. Deep-cycle batteries are considered durable enough to withstand repeated discharging of 80 percent of their total capacity, or 80 percent “depth of discharge” (DOD).
Batteries used in off-grid applications are often heavily cycled at partial states of charge, meaning that energy is drawn out of them over the course of a day or more, followed by some recharging, but it may be several days, or even weeks, before they’re fully recharged. This is especially hard on lead-based batteries, and also makes it difficult to interpret the manufacturer’s battery cycle life chart to predict longevity. It may be tempting to predict that average seven-year battery life expectancy (2,555 cycles) translates to an average DOD of 35 to 40 percent, but many factors are at play. Ultimately, lead will shed from the electrodes, depleting them quicker during periods of high discharge rates, partial charge levels, or elevated heat.
LFP batteries have a considerably greater lifetime than FLA batteries, with far more charge and discharge cycles available, and less dramatic partial charge degradation.
Battery capacity is typically expressed in terms of how many amperes (amps) of current can be delivered over a period of time. For example, a common deep-cycle lead-acid battery indicates that it can deliver 75 amps for 115 minutes. A more meaningful capacity term is the amp-hour (Ah), which expresses how many hours a battery can deliver energy until its specified end-point voltage is reached and the battery dies. Battery spec sheets provide ratings that reflect the capacity at different discharge rates over time, less energy is available from the battery at higher discharge rates.
Ah tells us how many amps a battery can deliver over time at a certain rate, but it doesn’t fully quantify the energy stored in a battery. Energy is power (watts) delivered over time (hours). Watts are calculated by multiplying volts by amps. The 225-Ah, 6-volt example above can be wired in series to achieve the required battery bank voltage. Since Ah already has a time factor built in, all we have to do is multiply 6 volts by 225 Ah to get 1,350 watt-hours (Wh). Divide Wh by 1,000 to express energy storage capacity in the more familiar term of kilowatt-hours (kWh), which is how electric companies bill us for the electricity we consume. For perspective, a 100-watt lightbulb that’s lit for 10 hours consumes 1,000 Wh, or 1 kWh.
A wide variety of sizes and capacities are available for LFP batteries. Case configurations make direct replacement of FLA possible. Because of the higher charge and discharge rates possible with LFP, you may see fractional C-values (such as 0.5C), which indicate a charge or discharge period of under an hour.
Charge and Discharge Dynamics.
Charge and discharge dynamics in FLA batteries are driven by lead-based electrode plates immersed in a sulfuric acid and water electrolyte solution. As the battery is charged, lead oxide builds up on the positive plates, and the electrolyte becomes stronger. During discharge, the electrolyte solution grows weaker as both electrodes become lead sulfide, having absorbed sulfuric acid from the electrolyte. During discharge, the voltage drops predictably. The state of charge of an FLA battery can be determined by reading the resting voltage of the battery. Battery voltage in conjunction with a hydrometer reading of the specific gravity of the electrolyte in each cell can reveal a lot about the state of charge and overall health of an FLA battery.
The charge and discharge dynamics in LFP batteries differ from FLA in terms of the electrochemical process, but can be described in a similar way. During discharge, positively charged lithium ions move within lithium salt electrolyte from the negative electrode to the positive electrode. Electrons are carried from the negative electrode, through the electric circuit, and back to the positive electrode. One big difference between FLA and LFP batteries’ reactions is that FLA chemistry happens on the surface of the lead electrodes, while ions in the non-liquid electrolyte of LFP batteries are fully absorbed into the crystalline structure of the electrodes.
You can’t easily determine the state of charge of LFP batteries with a voltmeter, because the battery voltage remains fairly constant over a wide range of discharge depths. Those who switch from FLA to LFP may find this, a bit flummoxing. When the voltage finally drops, it means the battery needs to recharge. The best way to understand and manage charge cycling is to use a properly calibrated monitor that tracks energy going in and out of the battery bank. Because of the sensitive nature of LFP chemistry and tight limits on charge and discharge parameters, manufacturers provide an electronic battery management system (BMS) to help prevent charge- and discharge-related battery damage. The BMS may also include a capacity monitor.
Charging must be performed using the proper “charge profile,” meaning the correct voltage and current for a prescribed amount of time to rejuvenate a battery’s chemistry, ensure maximum lifetime, and avoid potentially catastrophic failure. Voltage and current requirements change over the course of the charge cycle. As a battery fills up, the charge current needs to decrease to avoid overheating. If the current is too high, the battery heats up. When the battery heats up, it accepts a charge faster and heats up even more. Soon, the battery is in “thermal runaway,” and its life will be significantly reduced in a very short time.
Typically, FLA charge current shouldn’t be much more than 10 percent of the capacity rating, though higher current can be tolerated if the temperature is closely monitored. Periodically, FLA batteries should be “equalized,” which is a controlled overcharge that helps reverse sulfation (lead sulfate crystal growth) on the plates. Most modern battery chargers are sophisticated enough to manage a complex three-stage charge profile automatically.
In LFP batteries, charging is the reverse of discharging in terms of ion and electron transfer. Most modern off-grid battery chargers (solar and inverter-integrated) are adjustable to accommodate the specific LFP charge profile. This is essentially a two-stage charge consisting of bulk and float charges. Conventional FLA charging schemes don’t belong in the LFP world. That is, no equalizing, trickle charging, or temperature compensation should be used. LFP batteries have a very low internal resistance and can accept very high charge currents, resulting in faster recharge times. An LFP battery’s BMS is designed to prevent damage due to overcharging and over-temperature operation.
FLA batteries average about 75 percent efficiency, meaning 25 percent more energy needs to be put into an FLA battery than was taken out to fully recharge it.
LFP efficiency is in the range of 95 to 98 percent, resulting in shorter charging times and higher current delivery to the load with much less heat. More efficient charging means a smaller, less costly PV array, fewer hours on the generator, and lower energy cost if you charge batteries from the grid.
In addition to proper charge and temperature management, FLA batteries need to have their electrolyte checked and refilled monthly. You’ll probably need to clean corrosion off some of the terminal connections as well; applying anti-corrosion grease or spray will help. Be aware that when FLA batteries are in a partially discharged state for any length of time, or if the electrolyte dips low enough to expose the plates to air, sulfation will occur rapidly, insulating the plates against the required chemical reactions. Sulfation is difficult, if not impossible, to reverse if the battery isn’t properly maintained.
Maintenance for LFP batteries amounts to checking and tightening connections as needed. There’s no electrolyte to check, and corrosion isn’t a problem for LFP batteries.
Why Choose Aolithium Battery for Yourself?
After reading the above introduction, we have a question: Is there a LiFePO4 battery on the market with all the advantages above?
Aolithium LiFePO4 battery may be your ideal answer.
Aolithium LiFePO4 batteries come with all the best features you want in a Lithium Battery, along with an 3-5 years warranty period. We use Lithium Iron Phosphate (LiFePO4), which is the gold standard in lithium battery technology. The following are the best features Aolithium Lithium batteries give you.
Bluetooth 5.0 Mobile App Monitor in Real-time
Smart Bluetooth 5.0 Mobile App monitoring from your phone, so you can know exactly what your battery data is at any time.
Data in real-time includes:
- Battery state of charge in *% (SOC)
- Estimated charge / run time
- Charge / discharge switch
- Balance / protection state
- Battery voltage
- Charge / discharge current
- Battery temperature
- Remaining capacity
- Number of charge/discharge cycles
- Average voltage
- Rated power
Integrated Battery Management System (BMS)
The battery protection board has a strong load capacity, and the continuous discharge current can reach up to 200A. BMS protection functions include a 4 battery-cell series protection, charging and discharging protection, hardware protection for discharge overcurrent and short circuit, software protection for Overvoltage, Undervoltage, Temperature, Overload, accurate SOC calculation.
Revolutionary Battery Pack Technology
- Durable ABS case that is non-flammable.
- High-efficiency laser welding of automotive-grade power batteries for cell busbars.
- Customized thick copper bus connections inside to assure over-current capability and reduce cross-polarity.
- Advanced mounting plate and bolt technology to maintain battery stability.
Aolithium 12V100Ah LiFePO4 battery has a minimum of 4000 cycles time, and the design life is up to 10 years. Even after 4,000 cycles at 90% DOD, they’re still capable of producing 70% of the rated capacity. Meanwhile, lead-acid batteries are only left with 50% of rated capacity after they hit their 300th to 500th cycles’ life.
You don’t need to buy different batteries for different uses. Aolithium LiFePO4 batteries can handle just about any deep cycle applications, such as RV, van, camper, marine, camping, off-grid, solar home, UPS backup, golf cart.
Our batteries are certified with ISO9001/UL/CE/UKCA/UN38.3 and meet all US & International air, ground, and train transport regulations. Aolithium uses the best cells, so your Battery lasts longer and performs better. All cells are fully listed and meet the UL1642 standards.
Life is more than just a journey; it is an adventure you go on and grow through the hardships it presents while being away from home. However, getting to travel the world but from the comfort of your home is what having an RV feels like. To be able to experience such a blessing is impossible if your home has no power.
With so many options and complications with each to power your home, Aolithium Lithium Batteries (LiFePO4) simplifies it all and provide you with the peace of mind you deserve with the capability to power your ideal RV experience.