In our previous guide, we explained how power stations with a dedicated Extra Battery Port can be expanded using cheaper LiFePO4 batteries, along with the cost savings and the trade-offs involved compared with official expansion batteries. That approach works well, but it depends on having a purpose-built expansion port. For power stations that only offer a solar input and no dedicated expansion interface, there is another viable path. This article explores how an external LiFePO4 battery can be connected through the solar input by using a DC-DC converter to present the battery as a high-power solar source, allowing the power station’s existing charging system to accept and manage the additional energy.
Technical Principle
The solar input on a power station is fundamentally a direct current input designed to accept a stable DC source within a specified voltage window. A LiFePO4 battery is likewise a DC source. Therefore the engineering goal of the solar-input expansion method is simple and precise. Present the external battery to the solar inlet as a stable DC supply whose voltage and current lie inside the station’s allowed limits. As long as the incoming DC voltage remains within that window, the station’s internal charging circuitry will treat it as a valid energy source and route it to charge the internal battery. The origin of that DC power, solar panel or battery, is electrically irrelevant.
From this perspective, an external LiFePO4 battery is simply another DC source. The role of the connection method is to ensure that the battery’s output voltage and current are presented to the solar input in a safe, regulated form.
There are two distinct electrical scenarios.
If the external LiFePO4 battery’s voltage, including its fully charged voltage, already lies within the solar input’s allowable range, the system is electrically straightforward. The battery can act as a stable DC source feeding the solar input through a properly rated cable and mandatory DC protection devices. In this case, no DC-DC conversion is required. The power station will accept the input just as it would accept a solar array operating at a fixed working point.
If the battery voltage does not fall within the solar input range, a DC-DC converter becomes mandatory. Its purpose is precise and limited. It converts and regulates the battery’s native voltage to a fixed output that the solar input can safely accept. The converter should be configured in constant-voltage, current-limited operation so that the output voltage never exceeds the solar port’s maximum rating and the current stays within safe limits. It is performing voltage adaptation and stabilization, not simulating solar behavior.
Internally, the power station does not distinguish between DC coming from a solar panel or DC coming from a converter. As long as voltage and power limits are respected, the charging circuitry processes the input normally and charges the internal battery accordingly.
Understanding this principle is critical. The success of this method depends entirely on voltage compliance, power limits, and proper regulation. When those conditions are met, the solar input becomes a flexible and cost-effective path for integrating an external LiFePO4 battery, even on power stations that lack a dedicated Extra Battery Port.
Power limit (solar input max)
The solar input’s rated maximum power and current set the hard ceiling on how much energy can flow through that port. No matter how large your external LiFePO4 battery or how capable your DC to DC converter is, the solar inlet limits the charge or supply rate the power station can accept.
A few practical points to keep in mind:
- Treat continuous ratings, not brief peaks. Many batteries and converters can tolerate short surges, but continuous current determines heating and long-term safety.
- Leave design margin. Specify converters and wiring with headroom above the target current so devices run cooler and protections do not nuisance-trip. A common rule is to allow 15% ~ 25% margin on continuous current.
- Watch thermal limits. Undersized connectors or cables will heat, causing resistance to rise and effective transfer to drop, and they can damage insulation or contacts.
- Account for efficiency. DC to DC converters are not lossless; convertor efficiency reduces net power delivered to the power station, so size the converter accordingly.
Example for clarity: if the power station solar port is rated 700W at a 51.2V system, the maximum continuous current available across that port is 700 ÷ 51.2 = 13.67 amps, roughly 13.7A. Even if the battery or converter can provide 40A, the host will only accept about 13.7A through that inlet.
