My Gear of Choice:
Jump below to see What Gear Makes the Cut in my Ham Shack
As a licensed ham, I rely on lithium iron phosphate or LiFePO4 batteries to keep my gear running 24 hours a day. In fact, I am continuously on backup power. I have utility available but if I can, I prefer to keep the shack off-grid. I get AC power from a 2,000-watt inverter connected to a bank of LiFePO4 batteries, in turn fed from a solar charge controller and a half a dozen 100-watt panels.
I use my inverter 24 hours a day and that means maintaining my batteries is vital to the operation of computers, a small refrigerator, lights, some USB chargers, and a 30-amp switching power supply for my ham gear. There are a lot of articles on the topic of battery charging out there, but in this post I will focus on the unique situation I find myself in, whereby I have lots of battery capacity and not enough solar to achieve a full charge every day during winter.
It’s these times that I need to connect a utility-powered battery charger to top off my batteries and trigger a balancing routine by the battery’s onboard management system (BMS). But how often do I need to pay for a grid charge? It’s a balancing act in winter as I watch my state-of-charge oscillate in an ever downward trend.
LiFePO4 batteries have a unique charge curve, shaped like two inverted hockey sticks taped together in the middle. This curve maintains relatively steady voltage throughout the bulk of charging but as state-of-charge approaches 90%, battery voltage quickly rises until they reach full charge at 3.65 volts per cell or 14.6 volts for a 12.8 volt battery, typically assembled from four cells. To accommodate this power curve, you really need a purpose-built charger, one specifically designed to handle the unique charge characteristics of LiFePO4 batteries. You need a charger that can get to and hold 14.6 volts in order to achieve what is considered a full charge.
LiFePO4 battery chargers will bring a battery up to 14.6 volts and hold it there for several minutes before disengaging or switching to float mode. At this point, you should be able to measure 14.6 volts at the battery terminals using a multi-meter. I have found that most utility-powered LiFePO4 chargers do not have a float function, they simply go idle after completing a charge routine.
Solar charge controllers, on the other hand, usually do have a float mode that holds the battery just below its natural resting voltage of about 13.6 volts. The Victron solar charger floats at 13.5 volts by default when using the Smart Lithium preset. Float is valuable with solar chargers because it assumes you are in an off-grid situation and want to maintain a known state-of-charge as long as possible.
Understanding the LiFePO4 Charge Curve
The LiFePO4 battery charge profile differs from traditional lead-acid or lithium-ion batteries. It uses a constant current bulk charge then switches to a constant voltage absorption phase. Most solar chargers and some line-powered chargers have a third “float” stage that maintains batteries in a slightly discharged state after adequate time at full charge voltage.
The flat discharge curve provided by this amazing battery chemistry also means they stay at a steady voltage for most of their usable discharge capacity, making it tricky to estimate remaining charge without a proper battery monitor like a smart shunt or hall-effect clamp meter that can track power over time.
It’s this flat discharge curve that makes these batteries so valuable as a standalone power supply for ham radio operators. Unlike lead acid batteries that start losing voltage immediately, and eventually rob your gear of power, LiFePO4 maintains a nearly constant output voltage and reliable current current reserve until around 20 percent state-of-charge, when voltage enters a sudden and rapid decline. The two stages of charging, plus float, are described below:
LiFePO4 Battery Charging Stages
Stage #1
Bulk Charge
Constant
Current
The charger delivers a steady high current while battery voltage rises. This phase handles the bulk of the charging, typically bringing the battery to around 80-90% of its capacity.
Stage #2
Absorption
Constant
Voltage
Once the voltage reaches the charger’s set limit, usually 14.4 to 14.6 volts, the charger maintains this voltage, while gradually decreasing current. This phase slowly “tops off” the battery and is critical as it provides adequate time and power for active cell balancing to take place.
Stage #3
Float
Reduced
Voltage
After the entire bulk charge and absorption stages have completed, the last stage for some chargers is float. In this mode, charger voltage is reduced to below the battery’s natural resting voltage. This minimizes long-term wear while holding the battery at a known state-of-charge in preparation for future use.
Take Steps to Ensure Proper Cell Balancing
LiFePO4 batteries use onboard BMS systems to manage safety and performance, including keeping the internal cells well balanced. This means keeping the voltages of the internal cells within close proximity of one another. However, balancing only occurs when the battery reaches its full charge. This is why periodic full charges are necessary.
BMS systems usually start balancing when the pack reaches 14 to 14.2 volts. This allows ample time for balancing to take place while the battery closes in on full charge at 14.6 volts. Most “smart” batteries during this stage actively transfer energy from one cell to another in order to put them back in balance. Other batteries may balance cells by “burning off” excess charge through resistance in order to get all cells at the same voltage at the same time.
Tips For Proper LiFePo4 Balancing:
📈 Monitor Charging Current
Once your charger switches to constant voltage mode, watch for the current to taper down to nearly zero (typically below 0.05C, or 5% of the battery’s capacity). If the current never drops to this level, balancing may not occur.
👍 Confirm Balancing with a Multi-meter
Allow the charge cycle to complete and the batteries to rest with no load or charge current for one hour. Measure the voltage of individual batteries within the string. Batteries that are balanced internally will have nearly identical voltages, usually within 0.01V of each other.
💯 Charge to Completion Every 20 to 30 Cycles
A full charge isn’t required every cycle. For daily use, charging to around 80-90% can extend lifespan, although many claim that rule does not apply to LiFePo4. I aim to get a full charge every two to three weeks to activate balancing. If you have Bluetooth batteries, you will see a notice when it’s time to balance. Check your owner’s manual for the minimum recommended full charge interval for your specific battery.
Knowing When to Connect a Utility-Powered Charger
Because I’m powered only by solar and battery, there are times, especially in winter, when I run a power deficit. I may squeak out a little bit of charge during the day, but it doesn’t get me back to the battery voltage I started at that morning when the new solar charge cycle started. While solar power is a fantastic way to keep batteries topped up in the field, relying on solar power for your daily operation is a different story and requires some planning and compromise.
Long rows of dark days can cause my state-of-charge to drift lower and lower until I have no choice but to connect an external power source. It’s not a problem because I do have utility power nearby, and I honestly don’t mind the occasional boost in the dead of winter. Knowing when to charge is key. I don’t want to pay for expensive grid power if I don’t need to, but I also don’t want leave myself without reserve in the event we actually lose grid power and I find myself using battery as my primary power source. That’s why I’ve made the decision to oversize my battery bank at the risk of not being able to achieve a full charge each day. That may not even be important in the long run.
Part of our responsibilities as good stewards of our batteries is not allowing them to discharge too deeply, even though LiFePo4 can be discharged until the BMS turns off. Knowing when to connect a utility-powered charger is essential to prevent our batteries from discharging too deeply. There are four key indicators to watch out for:
LiFePO4: Key Indicators That It’s Time to Charge
📉 Voltage Drops Below 12.8V
LiFePO4 batteries maintain a steady voltage for most of their discharge cycle. However, once the voltage dips below 12.8V, you’re nearing the last 20% of capacity. It’s time to plug in to avoid deep discharge. Let the battery rest for 30 minutes with no load before taking a voltage measurement.
😓 Reduced Performance of Connected Devices
If your radio or other equipment starts showing signs of power deprivation, for example, the display dims or blanks out when you transmit, or if you hear relays clicking repeatedly, it is definitely time to check battery voltage and get a charger turned on.
⚠️ Charge Controller Not Reaching Cutoff Voltage
Use a solar charge controller with a display to track solar input and battery status. If your charge controller is unable to bring battery voltage to 14.6 during a single charge cycle or if it never switches to “float” mode, then you are not getting a full charge.
🥶 Seasonal Adjustments
In winter or during prolonged periods of cloudy weather, you may need to rely on utility charging more frequently to prevent undercharging and ensure periodic cell balancing. If you rely on your batteries for emergency backup in the event of a power failure, your priorities are to embrace utility charging during times of bad weather in order to stay topped off and be prepared.
LiFePO4: Tips for Effective Charging
⚡ Use a Dedicated LiFePO4 Charger
These chargers are designed to provide the two-stage—constant current, then constant voltage—charging requirements of LiFePO4 batteries. LiFePO4 does not require an equalization phase, as balancing is automatically controlled by the onboard battery management system.
🥵 Avoid Overcharging
Most LiFePO4 chargers go idle after completing a full charge cycle. It should not hold your battery in a fully charged condition for an extended period of time. If it does, unplug it immediately after it finishes. Most onboard BMS systems begin balancing at 3.5 volts per cell or 14 volts for a 12.8-volt battery. A fully charged LiFePO4 should never exceed 14.6 volts.
🛑 Monitor Depth of Discharge
Avoid running your battery down to the point that the BMS disengages. If possible, use an external shunt to measure actual watts consumed over time. Some shunts even have Bluetooth capability. This is one of the better ways to track capacity and depth of discharge. If relying on a multi-meter to determine state of charge, measure at the battery terminals with no load for best accuracy.
🧐 Leverage Smart Monitors
A good smart shunt with Bluetooth or a hall-effect clamp meter are two of the most accurate ways to measure energy as it flows in and out of your battery. If you don’t have one or more of these devices, considering adding them to your data gathering arsenal. Knowing your state-of-charge is important and these devices will give you the insight you need.
My Gear of Choice
Here’s a list of the items discussed in the above article. These are items that I use and trust in my ham shack 24 hours a day, every single day. Affiliate links below:
| What I Like | Why I Like It |
| Gaindel 2,000-watt Inverter | FCC certified, low EMI, soft start, 125VAC output |
| CycleNBatt 100AH LiFePO4 Mini Battery | Best deal around for high quality prismatic cells |
| 20A LiFePO4 Smart Charger | Noisy but effective; good for top charging |
| Victron Energy 100-volt 50-amp SolarSmart Charge Controller | Best in class MPPT, efficient harvesting, good for LiFePO4 |
| Renogy 1,000-watt Inverter | Reliable, 114VAC output |
| Renogy 100-watt Solar Panel 2-Pack | Sturdy, reliable, and efficient. (I have 8 panels, total) |
Final Thoughts
LiFePO4 batteries are a total game changer and I am so onboard it’s not even funny. I’ve been accumulating battery capacity for a year now and have confidence that I can run 24 hours a day through all seasons and conditions, even if that does mean running down my batteries over a period of days once in a while. After all, I can always plug in to a utility-powered battery charger. Knowing when to charge boils down to having good information. A good calibrated shunt or hall-effect meter are important to keeping your battery ready to go.
Their unique charge curve makes LiFePO4 efficient and durable, but understanding how to charge them effectively is crucial for longevity. By monitoring your battery’s voltage, ensuring proper balancing, avoiding overcharging, and adjusting your charging strategy to include utility-powered charging when needed, you can keep your power setup reliable and long-lasting while also minimizing time wasted and money spent taking power from the grid.
This article contains affiliate links.