In Japan, where natural disasters such as typhoons and earthquakes occur frequently, securing emergency power supplies to survive the ``72 hours (three days) after a disaster occurs’’ is an urgent issue until infrastructure restoration. Gathering information, confirming safety, serving as a flashlight, and maintaining the battery of your smartphone are a lifeline. However, small everyday batteries (5,000-10,000mAh) cannot power the entire family. In this article, we will use concrete simulations and checklists to explain how to choose a high-capacity mobile battery that will be truly useful in times of disaster.
Required capacity simulation to survive 3 days of power outage
If one person fully charges a typical smartphone (battery capacity approximately 3,000 to 4,000 mAh) once a day, approximately 10,000 to 12,000 mAh is required for three days. What must not be overlooked here is “conversion loss.” When converting the battery internal voltage (3.7V) to the USB power supply standard (5V, etc.), approximately 30-40% of energy is lost as heat. Therefore, the actual effective capacity that can be extracted from a product with a stated capacity of 20,000mAh is approximately 13,000mAh (about 3 to 4 times a smartphone). If you are living in an evacuation zone with two or three family members, it is realistic to secure at least two 20,000mAh units or a 30,000mAh class ultra-high capacity model.
Essential specifications required for disaster prevention batteries [5 criteria]
- Rapid input speed (PD compatible): It is extremely important to be able to charge the battery quickly. Choose a model with 30W to 65W or more that supports USB PD input, so you can quickly charge the device using the limited power outlets at water stations and evacuation centers.
- Multiple ports output simultaneously: Ideally, it should have 3 or more ports, including USB-C and USB-A, so you can charge your family’s smartphones, LED lanterns, etc. at the same time.
- Pass-through power supply function: A function that allows you to simultaneously charge the connected smartphone while charging the battery itself. It shows its true value in situations where there is only one outlet.
- Equipped with low current mode: This feature allows you to charge small devices such as smart watches, hearing aids, and small radios without causing protection shutdowns due to overcurrent.
- Remaining power digital numerical display: Instead of a 4-level LED indicator, a percentage display in 1% increments makes it easier to plan power distribution.
“Lithium iron phosphate” and rolling stock operation
Batteries that use lithium iron phosphate (LiFePO4) as the positive electrode material have been attracting attention in recent years. Compared to general ternary lithium, the risk of ignition is extremely low, and the charge/discharge cycle life is 3 to 4 times longer (approximately 2,000 times or more). In addition, the self-discharge rate when left unused is low, making it suitable for long-term storage. Instead of leaving it sitting at the bottom of your disaster prevention bag for years, use it on a daily basis during your travels and outdoors, and keep it in a “rolling stock” mode to keep it close to fully charged at all times. Of course, be sure to check whether the product has the round or diamond-shaped “PSE mark” that meets the Electrical Appliance and Material Safety Act.
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