Predictable Power Supply Needed to Keep the System Always Operating

Smart home technology is rapidly growing and being adopted. Millions of homes are installing systems such as video doorbells, remote camera monitors, and security control panels, and this number will continue to increase at an even faster pace in the future.

While older security systems simply sounded an alarm when an intrusion occurred, today's systems allow users to remotely monitor various locations in their homes via smartphones, offering higher convenience and utility. Here, "smart" ultimately means "connectivity." In order to deliver video content from a remote camera to a smartphone, a certain form of communication is required.

Because these applications are characterized by safety and security, the system must have high reliability, and for this to be achieved, predictable power is needed to keep all system components operating at all times.

Many devices used in smart home systems are connected to household AC power, but for remote cameras and other equipment to be used in various locations including outdoors, it may be more appropriate to operate the complete product with a battery. To maintain trust in such "always-on" systems and achieve continuous communication, intelligence for monitoring and maintaining the battery and power system must be added. At a minimum, users should be able to receive alerts or notifications about problems when they occur. Furthermore, the system should be able to continuously monitor both the charge state and health state of the power supply.

How can we check and report the battery's state of charge and, more importantly, the battery's state of health? This task is best accomplished using a dedicated battery fuel gauge device.

First, let's understand the difference between state of charge (SOC, remaining charge) and state of health (SOH, aging level). We are always concerned about the state of charge—whether the battery is full, empty, or how much remains. In the case of smartphones (which have a built-in battery fuel gauge), the battery will be charged and discharged more than once a day. However, in smart home applications, especially when connected to AC power, the state of charge will remain close to 100% almost always. The battery is used as backup power in case the AC power is interrupted. Therefore, in these applications, state of charge is not always the most useful parameter to track.

State of health (SOH) indicates how well the battery performs its function in the application compared to when it was new. For example, suppose an application started with a 1000mAh cell. Depending on operating conditions or environmental conditions, after one to two years, the effective capacity of this cell may degrade to 850mAh. Then the state of health would be 85%. This means the battery is performing 85% as well as it did when new. While battery characteristics vary, typically once the state of health drops below 70-75%, battery capacity degrades rapidly. Consequently, for safety and security related applications, when the battery state of health reaches 80%, it is time to replace the battery.

For example, consider a system that can operate at a minimum battery voltage of 3.4V. Under these conditions, an aged battery can provide energy for only about one hour. In contrast, a new battery can last about 1.7 hours.

Through good charge management, a rechargeable battery can be recovered multiple times from a completely depleted state to a fully charged state, but in this process, degradation occurs for various reasons. The primary reason is repeated charging and discharging cycles, but another reason is exposure to heat.

A camera with an embedded battery operating outdoors can be exposed to high temperatures for extended periods. Some cameras use solar panels to recharge the battery. While this method is useful for implementing off-grid applications providing wireless connectivity, it requires installation in a location with strong sunlight, which means prolonged heat exposure that can accelerate battery cell performance degradation.