Hardware Reference
In-Depth Information
Table 18.31
lists the specifications of the common 20mm diameter lithium coin cell bat-
teries you might find in a PC.
Table 18.31 Common 20mm Lithium Coin Cell Specifications
Estimated battery life can be calculated by dividing the battery capacity by the average
current required. For example, a typical CR2032 battery is rated 220 mAh (milliamp
hours), and the RTC/NVRAM circuit in most current motherboard chipsets draws 5 μA
(microamps) with the power off. Battery life can therefore be calculated as follows:
220,000 μAh ÷ 5 μA = 44,000 hours = 5 years
If a thinner (and lower-capacity) battery such as the CR2025 is used, battery life will be
shorter:
165,000 μAh ÷ 5 μA = 33,000 hours = 3.7 years
Batterylifestartswhenthesystemisfirstassembled,whichcanbeseveralmonthsormore
before you purchase the system, even if it is new. Also, the battery might be partially dis-
