C10 vs C20 Battery Rating Explained

One of the most widespread confusions in the Indian energy storage market is the difference between C10 and C20 rated batteries. Retailers often sell both as "200Ah batteries," but their actual usable energy under solar operating conditions differs significantly.

1. What Does "C-Rating" Signify?

The "C" rating denotes the discharge time in hours over which a battery delivers its nominal rated capacity down to a cutoff voltage (usually 10.5V):

C20 Rating (Home Inverters): The battery delivers its rated capacity over 20 hours. For example, a 200Ah C20 battery discharges at a slow rate of 10 Amperes (200 ÷ 20 = 10A).

C10 Rating (Solar Photovoltaic): The battery delivers its rated capacity over 10 hours. A 200Ah C10 battery discharges at 20 Amperes (200 ÷ 10 = 20A).

2. Peukert's Law and Rapid Discharge

Due to Peukert's Law, the faster a lead-acid battery is discharged, the lower its deliverable energy capacity:

If you discharge a C20 battery in 10 hours, its usable capacity drops by 10% to 15% (a 200Ah C20 battery yields only ~170Ah to 180Ah at a 10-hour rate).

In contrast, a Flash Horse Power 200Ah C10 Solar Battery is built with thicker plates and higher active mass density specifically engineered to deliver a true 200Ah even under high-rate 10-hour daytime solar cycles.

3. Which Rating Should You Purchase?

Choose C20 for Home Inverters: When power outages are sporadic and discharge rates are low to moderate.

Choose C10 for Solar Applications: Solar panels only charge for 6-8 peak sunlight hours, and battery banks frequently supply heavy loads overnight. A true C10 rating ensures optimum cycle life and zero capacity throttling.