PERFORMANCE CHARACTERISTICS  
The simple overall performance characteristics, which have an impact on the battery design, are as follows:  
• Charge/discharge (C/D) voltages  
• C/D ratio  
• Round-journey strength efficiency  
• Charge efficiency  
• Internal impedance  
• Temperature rise  
• Life in range of C/D cycles  
3.4.1 C/D VOLTAGES  
The mobileular voltage version in the course of an average C/D cycle is proven in Figure 10.five for a mobileular  
with nominal voltage of 1.2 V, together with Ni-MH and Ni-Cd. The voltage is most whilst  
the mobileular is absolutely charged (SOC = 1.zero or Ah discharged = zero). As the mobileular is discharged, the  
mobileular voltage (Vc) drops speedy to a plateau fee of 1.2 V, which holds for a protracted time  
earlier than losing to 1.zero on the stop of capacity (SOC = zero). In the reverse, whilst the mobileular is  
recharged, the voltage speedy rises to a plateau fee of 1.forty five V after which reaches a  
most fee of 1.fifty five V. The C/D function additionally relies upon on how rapid the battery is  
charged and discharged.  
3.4.2 C/D RATIO  
After discharging a sure Ah to load, the battery calls for extra Ah of price to restore  
the entire SOC. The C/D ratio is described because the Ah enter over the Ah output without a net  
alternate withinside the SOC. This ratio relies upon at the price and discharge prices and additionally on  
temperature, as proven in Figure 10.7. At 20°C, for example, the C/D ratio is 1.1, meaning  
the battery wishes 10%3.4.10 RANDOM FAILURE  
The battery fails while as a minimum one mobileular in a sequence fails. Cell failure is theoretically defined  
because the circumstance wherein the mobileular voltage drops under a sure price earlier than discharging  
the rated potential at room temperature. The price is normally taken as 1.zero V in cells with  
nominal voltage of 1.2 V. This is a completely conservative definition of battery failure. In  
practice, if one mobileular indicates much less than 1.zero V, different cells could make up the distinction without  
detecting the failure on the battery level. Even if all cells display solid voltage under 1.zero V  
at complete load, the burden may be decreased to hold the preferred voltage for a while until  
the voltage degrades further.  
The mobileular can fail in open, brief, or be in a few intermediate state (a smooth brief). A brief that  
begins offevolved smooth subsequently develops right into a tough brief. In a low-voltage battery, any strive to  
fee with a shorted mobileular may also bring about bodily harm to the battery or the fee  
regulator. On the opposite hand, the shorted mobileular in a high-voltage battery with numerous  
series-related cells may fit forever. It, however, loses the voltage and ampere-hour  
potential, and hence, might paintings as a load at the wholesome cells. An open mobileular, on the opposite  
hand, disables the complete battery of series-related cells.  
In a device having  parallel batteries (a not unusualplace layout practice), if one mobileular in one  
battery receives shorted, the 2 batteries might have extraordinary terminal characteristics.  
Charging or discharging such batteries as a collection can bring about quite choppy current  
sharing, eventually is overheating one of the batteries. Two treatments are to be had to