Rechargeable Batteries

A battery can be recharged by pushing current into it at a controlled rate, $I_r$.

Higher amount of current $I_r$ gives faster charging but can cause batteries to:

• Overheat
• Become permanently damaged
• Significantly reduce capacity

Recharging currents are specified in terms of the Battery Capacity:

$$I_r=P\times C_{total}$$

$P$ is a factor (units of $[{\text{h}}^{-1}]$) that depends on the chemistry of the battery.

For example NiMH batteries have $P=0.1$. If $C_{total}=2.1\text{ Ah}$, determine $I_r$:

$$I_r=P\cdot C_{total}=0.1\times 2.1=0.21\text{ A}=210\text{ mA}$$

Higher $I_r$ is possible with voltage, current, and temperature sensing. Usually, we can simply drop $I_r$ as SoC approaches 1.

“Trickle charging” maintains SoC, e.g. P = 0.01.