Solar road studs are an important type of road warning device. Their working principle is the same as that of other solar products. During the day, the solar panels on the top absorb light energy and convert it into electrical energy, which is stored in the battery. At night, when visibility decreases or in bad weather conditions such as rain and fog, the LED lights inside will automatically light up to guide passing vehicles and pedestrians to the edge and direction of the road.
Solar road studs generally use rechargeable batteries and achieve intelligent charging and discharging management through built-in controllers. This not only avoids overcharging and overdischarging of the battery but also maximizes the utilization of solar energy resources. The characteristic differences of different types of rechargeable batteries will directly affect the usage experience and overall cost of the road studs.
The performance of the battery directly determines the core indicators of solar road studs: continuous working hours, outdoor durability and long-term maintenance costs. According to industry data, approximately 60% of the faults of solar road studs are related to batteries. Therefore, battery selection is a key link in the reliability of the road stud system.
Lead-acid batteries are one of the earliest battery types to be applied in small solar lighting equipment. With mature production processes and relatively low manufacturing costs, they were widely used in early solar road stud projects. Its sealed design (SLA) solves the problem of acid leakage in traditional open-type lead-acid batteries, making it suitable for outdoor damp and dusty environments. It remains a common choice for budget-sensitive projects to this day.
Lithium batteries (especially lithium iron phosphate batteries LiFePO4) have been the mainstream upgrade solution in the field of solar led road studs in recent years. With the maturation of lithium battery technology and the decline in costs, its advantages of high energy density and long cycle life have gradually become prominent. Among them, LiFePO4 has become the preferred Lithium Battery type for outdoor solar road studs due to its superior safety compared to traditional lithium-ion batteries (such as ternary lithium), and has been recommended by institutions such as Lithium Battery Power, LLC as "an energy storage solution suitable for long-term outdoor recycling use".
When choosing solar road stud batteries, comparisons should be made around the following 9 core dimensions:
|
Indicator |
Description |
|
Energy Density |
Refers to the amount of electricity that can be stored per unit weight or volume, affecting battery performance in scenarios where size or weight is restricted. |
|
Effective Capacity & Depth of Discharge (DoD) |
Effective capacity is the actual usable capacity (nominal capacity minus the unusable part). DoD is the maximum allowable discharge ratio, determining the balance between usable power per cycle and battery lifespan. |
|
Cycle Life |
The number of times a battery can complete a full charge–discharge cycle. Battery life is typically measured by total cycle count or the point at which its capacity drops to a specified threshold. |
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Charging Efficiency & Charging Rate |
Charging efficiency refers to how effectively electrical energy is converted into usable power during charging. The charging rate determines the time required to reach full charge, especially important under short sunlight hours or rapid-charging conditions. |
|
Self-Discharge Rate |
The rate at which a battery naturally loses power when idle. A high self-discharge rate reduces available power after long periods without charging. |
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Temperature Tolerance |
Indicates the stability and safety of battery performance under high or low temperatures, affecting capacity, cycle life, and charge–discharge efficiency. |
|
Weight & Volume |
The impact of battery size and weight on road stud installation space, structural load-bearing capacity, and overall product dimensions. |
|
Initial Cost & Life Cycle Cost |
Compares the one-time procurement cost with the total cost over the entire service life, including maintenance and replacement, to assess cost-effectiveness. |
|
Safety & Maintenance Requirements |
Includes usage risks (e.g., thermal runaway, leakage) as well as daily or periodic maintenance needs, monitoring, and management requirements (such as the need for a BMS and replacement frequency). |
For solar led road studs, both installation space and road surface load-bearing capacity are practical issues that must be taken into account - most road studs have a diameter of only 10 to 15 centimeters and a height of 5 to 8 centimeters, and they also need to accommodate solar panels, controllers and light beads inside, leaving very limited space for batteries.
In terms of energy density, the advantage of LiFePO4 lithium batteries is quite obvious, typically reaching 90-160 Wh/kg, while lead-acid batteries only have 30-50 Wh/kg. Simply put, to store the same amount of electricity, the volume and weight of a lithium battery only require one third to one half of that of a lead-acid battery. For instance, to store 100 Wh of electricity, a LiFePO4 battery can handle it with approximately 0.8 kilograms, while a lead-acid battery requires over 2.5 kilograms. This not only takes up space but also increases the overall weight of the road studs. Moreover, it has higher requirements for the load-bearing capacity of the road surface during installation.
The road studs go through a cycle of "charging during the day and discharging at night" every day. Therefore, the cycle life of the battery and how much power it can discharge directly affect how often the battery needs to be replaced and how much money is spent in the long term.
First, let's look at the actual data: It is generally recommended that lead-acid batteries be discharged no more than 50%. If they are discharged too hard, their lifespan will drop rapidly. Under normal circumstances, they can be cycled 300 to 500 times. Calculated at once a day, they can last for about 1 to 1.5 years. Even when the LiFePO4 lithium battery is charged to 80%, it can still be cycled 2,000 to 3,000 times and last for 5 to 8 years without any problem. If a lead-acid battery is discharged by more than 50%, its cycle life will drop sharply from 500 times to less than 200 times, which means it needs to be replaced every half a year or so.
Calculated this way, the lifespan of a LiFePO4 battery is roughly equivalent to that of 4 to 5 lead-acid batteries. When the procurement cost is averaged out over each cycle, the "cost per cycle" of lithium batteries is only one-third of that of lead-acid batteries, which can save a considerable amount of money in the long run.
The outdoor weather is changeable. Sometimes it's cloudy and sometimes it rains continuously. This requires the battery to be able to store power efficiently and not to lose power easily.
The less energy loss during charging and discharging, the better. The charge and discharge efficiency of lithium batteries can reach 90% to 95%. For every 100Wh of electricity generated by a solar panel, approximately 90Wh can be stored in the battery. Lead-acid batteries have a lower efficiency, only 70% to 80%. When generating the same amount of electricity, the actual usable amount is much less.
In addition, the self-discharge rate of the battery when it is idle is also very crucial. The self-discharge of lithium batteries is only 2% to 5% per month. Even if it rains continuously for 30 days, more than 85% of the battery can still be retained, so the solar powered road studs don't have to worry about suddenly running out of power. Lead-acid batteries self-discharge quickly, losing 10% to 15% of their power each month. If they are left idle for a month, their battery level may drop to half, and they need to be recharged frequently; otherwise, the road studs might "go on strike" when a warning is needed. In projects in rainy areas, it has also been found that road studs powered by lithium batteries have far fewer malfunctions due to insufficient power than those powered by lead-acid batteries.
Solar led road studs are exposed to the outdoors all year round. In summer, the road surface temperature may exceed 60℃, and in winter, it can reach -30 ℃ in northern regions. The performance of the battery in extreme temperatures is very important.
At a high temperature of 45℃, the cycle life of LiFePO4 batteries can still maintain 80% of the nominal value, but that of lead-acid batteries is only 50%, and they are prone to sulfation of the plates, with their performance deteriorating over time. In a low-temperature environment of -10 ℃, the capacity of lead-acid batteries will drop to 40% to 50% of the rated value. When charging, the efficiency is less than 30%, and additional heating equipment must be added to use them. LiFePO4 batteries can still maintain a capacity of 60% to 70% at -10 ℃. However, a dedicated low-temperature charger is required; otherwise, lithium dendrites may form, affecting battery safety.
Overall, except for extremely cold regions with temperatures below minus 20 degrees Celsius, LiFePO4 batteries can basically adapt to temperature fluctuations in most areas, as long as they are paired with controllers with temperature compensation. The performance of lead-acid batteries will be significantly affected by both high and low temperatures.
When I first bought batteries, lead-acid batteries were indeed cheap. For instance, a 12V/7Ah lead-acid battery can be purchased for around 20 to 30 US dollars, while a LiFePO4 battery of the same capacity costs 50 to 70 US dollars, which is 2 to 3 times the price of a lead-acid battery. When the budget is tight, it is very easy to choose a lead-acid battery.
But when it comes to the long-term account, the situation is the opposite. Take a 12V/7Ah battery as an example: Lead-acid batteries can last for 1.5 years. After 5 years, they need to be replaced three times, which costs a total of 75 US dollars, averaging 50 US dollars per year. The LiFePO4 battery can last for 6 years and doesn't need to be replaced for 5 years. It costs a total of 60 US dollars, which is only 12 US dollars per year on average. Power-Sonic also mentioned that when replacing lead-acid batteries, roads need to be closed and road studs removed, and labor costs must also be taken into account. Especially on highways or in remote areas, the labor cost for a single replacement may even be more expensive than the battery itself. From this perspective, the life cycle cost of lithium batteries is actually only one quarter of that of lead-acid batteries, making them more cost-effective for long-term use.
From a safety perspective, both types of batteries have their own points to note. Although lead-acid batteries are technologically mature, they have two problems: First, they are prone to acid leakage. Even if they are sealed (SLA) types, the casing may crack under long-term vibration or high temperatures, and the acid can corrode the circuits inside the road studs. Secondly, a small amount of hydrogen gas will be produced during charging. If the outer shell of the road stud is sealed too tightly and the hydrogen gas cannot be discharged, there may be an explosion risk.
The safety of LiFePO4 lithium batteries is much better than that of traditional ternary lithium batteries. The thermal runaway temperature can reach over 200℃ (about 150℃ for ternary lithium), but a BMS (Battery Management System) must be installed. The BMS should be capable of overcharge protection (cutting off charging when the voltage exceeds 14.7V), overdischarge protection (cutting off power when the voltage drops below 10V), and over-temperature protection (alarming when the temperature exceeds 60℃). Otherwise, the battery may be damaged and there may even be safety hazards.
In terms of maintenance, lead-acid batteries need to be inspected frequently. Every 6 to 12 months, check if the casing is cracked and if the battery power is sufficient. When they are approaching the end of their lifespan, they should be replaced in time; otherwise, acid leakage will destroy the entire road stud. As long as the BMS of LiFePO4 lithium batteries is working properly, they basically do not require much maintenance. At most, the BMS function should be checked every 2 to 3 years. The maintenance cost is much lower than that of lead-acid batteries.
The compatibility of lithium batteries and lead-acid batteries varies significantly in different scenarios. The following are targeted recommendations:
|
Application Scenario |
Recommended Battery Type |
Main Reason for Recommendation |
|
Urban expressways and highways |
LiFePO4 lithium battery |
Long lifespan (5–8 years), low maintenance frequency, performs well in high-temperature environments, and reduces traffic impact caused by maintenance-related road closures. |
|
Remote areas (e.g., rural roads) |
LiFePO4 lithium battery |
Low maintenance requirements; no need for frequent manual replacement, helping avoid high maintenance costs in remote locations. |
|
Short-term projects (1–2 years construction period) |
Lead-acid battery |
Low initial cost; battery life matches the short project cycle, eliminating the need for long-term investment. |
|
Budget-sensitive small municipal projects |
Lead-acid battery |
Easy to maintain in accessible urban areas (e.g., sidewalks); allows cost control and reduces initial procurement pressure through regular replacement. |
|
Extremely cold regions (below –20°C) |
Lead-acid battery (with heating) |
Low-temperature performance of LiFePO4 is limited; lead-acid batteries with heating plates remain cheaper than low-temperature LiFePO4 alternatives. |
When purchasing solar led road stud batteries, it is necessary to carefully verify the following technical parameters and documents to ensure that the product meets the requirements:
Rated capacity (Ah, which needs to match the power of the road stud, for example, 5W road stud is recommended to be ≥7Ah), rated voltage (usually 12V, which needs to match the controller), maximum charging current (it is recommended to be ≤0.5C, for example, 7Ah battery ≤3.5A).
Recommended deep discharge (DoD), nominal cycle life (test conditions such as DoD and temperature should be specified), and temperature operating range (extreme temperatures in the project area should be covered).
For lithium batteries, it is necessary to confirm whether they are equipped with a built-in BMS and whether the BMS includes overcharge/overdischarge/over-temperature/short-circuit protection. For lead-acid batteries, it is necessary to confirm whether they are sealed (SLA) and whether they have a leak-proof design.
Battery housing protection grade (recommended ≥IP65, suitable for outdoor rain and dust).
UN38.3 (Lithium Battery Transportation Safety), MSDS (Material Safety Data Sheet), and RoHS (Environmental Protection Certification) need to be obtained from the supplier. For lead-acid batteries, CE certification is required as an additional requirement.
Capacity test, cycle life test, and temperature adaptability test reports before leaving the factory. If necessary, on-site sampling tests can be requested (such as three charge and discharge cycles to verify if the capacity meets the standards).
LiFePO4 batteries have a long cycle life (over 2,000 times), allow deep discharge (80% DoD), and have low maintenance requirements. Although the initial cost is high, the long-term life cycle cost is lower, making them suitable for the long-term use of outdoor road studs.
Yes. Lead-acid batteries have a low initial cost (only one-third of LiFePO4), making them suitable for short-term projects lasting 1-2 years or small projects with sensitive budgets. If maintenance is convenient (such as in urban areas), costs can be controlled by regular replacement.
To check the battery temperature operating range: If the local extreme high temperature is ≥45℃, LiFePO4 is preferred. For extreme low temperatures ≤-20℃, lead-acid with heating is preferred. If the temperature is between -10 ℃ and 40℃, both are acceptable. The choice should be made based on the lifespan requirements.
If a qualified BMS is built in, almost no maintenance is required. Only the BMS function needs to be checked every 2-3 years (such as whether the power is cut off normally during charging). If a BMS is not built in, the battery level should be checked every six months to avoid overcharging and overdischarging.
Yes. Acid can corrode the internal circuits and metal parts of the solar led road studs, causing short circuits or poor contact. Therefore, sealed (SLA) lead-acid batteries should be selected and the casing should be checked regularly for any cracks. If acid leakage is found, they should be replaced immediately.
In the design and procurement of solar road studs, the battery is the core component that determines the reliability and life cycle cost of the system. Overall, if long-term stability and the lowest maintenance cost are pursued, LiFePO4 (high-quality lithium batteries) should be given priority. If the budget is very limited and frequent replacements are acceptable, lead-acid is a lower-cost option in the short term. Do you need us to provide a comparative quotation based on the climate and power requirements of your project? Contact NOKIN for free technical consultation.
