Lithium Phosphate (LiFePO4) Battery Capacity Calculation Method

Compared with lead-acid batteries, lithium phosphate batteries (LiFePO4 or LFP) have many advantages. Longer service life, no maintenance, extremely safe, lightweight, improved discharge and charging efficiency, etc. The LiFePO4 battery is not the cheapest battery on the market, but due to its long service life and zero maintenance, it is the best investment you can make over time.

Many friends are stuck in the difficulty of choosing what capacity before buying LiFepo4 batteries. The formula for calculating the capacity of lithium iron phosphate batteries from theoretical and scientific research laboratories is as follows:

C= (e*N*n*1000) /(t*M)

Among them, e=1.602*10-19c, N=6.02*1023 pieces/Mol, n is the change in valence, and M is the molar mass (LFP is 157.76). F is the Faraday constant (96500 c/Mol), F=e*N.

This formula is a professional formula used by battery researchers in the laboratory. It is not easy to understand and not suitable for ordinary LiFepo4 battery purchasers. So is there a formula for calculating the capacity of lithium iron phosphate batteries for ordinary battery buyers?

The formula for calculating the capacity of lithium iron phosphate batteries for ordinary battery buyers can be used to quickly estimate the capacity of lithium iron phosphate batteries, which is only used for estimation. The formula is as follows:

Capacity = thickness * width * length * K (K unit is mAh/mm3)

The range of K value is (0.07~0.11). The K value depends on the size of the capacity. The larger the capacity, the larger the K value, the smaller the capacity, and the smaller the K value (it can be understood as the larger the size, the larger the K value).

In actual calculations, the K value can be set to 0.1 by default. For example, 103450 LP (thickness 10mm, width 34mm, length 50mm), calculated capacity=10*34*50*0.1=1700, the actual capacity is above 1800mah; for example, 603048 LP (thickness 6mm, width 30mm, length 48mm), calculated capacity=6* 30*48*0.1=864, the actual capacity can be 900mah.

The above is a quick method for estimating the capacity of lithium phosphate batteries, which is more convenient to use, but there are certain errors.