Most solar batteries have LED lights, digital displays, or voltmeters that directly report the state of charge. If the indication reading is 100%, then the battery is fully charged.
How do I know if my solar battery is fully charged?
Getting accurate charge readings and ensuring you don't over- or undercharge your battery is just one element of prolonging your battery's life. The simplest way of knowing whether your solar batteries are fully charged or not is to use your charge controller or inverter to check the battery's voltage.
You need to use a shunt resistor to also measure the solar panel's current while measuring the output voltage. You do not say how you know whether the battery pack is being charged or not. With your solar panel, if it has sufficient power to charge at all, it may take days of bright sunshine to charge the battery pack.
Solar charge controllers are designed to regulate the charging process of solar batteries, preventing overcharging and ensuring optimal battery life. They often incorporate various indicators to provide information about the battery's charge status. Here's how to determine if a solar battery is fully charged using a solar charge controller:
Step 3: Identity the fully charged LED: The controller should have a specific LED that indicates a fully charged battery. This is often the green or blue LED. Step 4: Assess the battery charge level: If the fully charged LED is illuminated, the battery is considered fully charged. If not, the battery needs more charging.
Measuring stationary solar batteries with a DMM voltmeter is best, but portable handheld voltage testers also work well. Built-in analog volt meters eliminate guesswork by reporting the actual battery voltage, which maps to the state of charge levels. However, the relationship between volts and charge percent varies by battery chemistry.
Charging time depends on: Under ideal sun conditions, size compatibly matched panels and batteries refill charge in 4-8 hours for lead acid or 2-3 hours for lithium ion. For example, a 400-watt solar panel system should fully charge a 400 Ah lead acid battery bank in about 8 hours at best solar irradiance.