Understanding Amperage from a 48V 200Ah Lithium-Ion Battery

To determine how many amps a 48V 200Ah lithium-ion battery can provide in one hour, we need to understand the relationship between the battery's Amp-Hour (Ah) rating and its discharge current.

Direct Amp-Hour Rating Calculation

A 200Ah battery can theoretically provide 200 amps for one hour. However, it can also provide a lower current over a longer period. This means that if you discharge the battery fully within one hour, it will deliver 200 amps at 48 volts for that hour. Conversely, if you draw 100 amps, the battery would last for two hours since 100 amps × 2 hours 200Ah.

Calculating Battery Capacity

The Ahr rating serves primarily for comparison, but it is influenced by the battery's chemistry. For a 48V 200Ahr battery, the capacity is 9600 Watt-hours (Wh). This means the total energy storage is 9600Wh. However, not all of this capacity can be fully used due to factors like discharge rate, temperature, and battery condition.

Real-World Application and Tapping Capacity

Let's consider that only 75% of this 9600Wh battery's capacity is usable. This means 7200Wh are available. To determine the current that the battery can provide, we use the formula: Power (W) Voltage (V) × Current (A). Therefore, if the load requires 7200W, the battery can deliver 7200W for one hour. This means current 7200W / 48V 150A.

C-Rating and Battery Performance

Batteries are often rated with a “C-Rating”. Typically, a 200Ah battery is expected to deliver 200A for one hour. However, with the 75% usable capacity assumption, the actual C-Rating would be 150Ah, which contradicts the nominal 200Ah figure. This means the battery's performance in real-world conditions may vary significantly.

Batteries can be very dynamic, and the C-Rating serves more as a figure of merit than an accurate performance indicator. This is because we do not typically discharge batteries at a uniform rate. Faster discharge rates lead to less total energy delivered, a phenomenon known as Peukert's Law. This complicates the understanding of battery capacity and performance.

The real value of C-Rating and discharge tests is to compare the current capacity of a battery over time. For instance, if a new battery can deliver 200A for one hour, a test repeated a year later can indicate how much the battery's capacity has degraded. This is useful for comparing new batteries of different chemistries.