How to choose the battery according to the application

　　Whether or not the end user is satisfied with the design of their portable device depends largely on the performance of the battery.

　　The key metric for batteries is, of course, battery life. On the surface, this is a simple specification, but it involves many factors, including: system load characteristics (time at full load current, partial current, and microampere current), power efficiency, system power management, battery type, and charging method.

　　In addition to the importance of the above performance itself, the interaction between these characteristics can also enhance or weaken the end user's experience. Generally speaking, when users start to notice the existence of the battery, things become more difficult! Good product design does not require frequent battery replacement (such as TV remote controls) or frequent battery charging (such as electric toothbrushes), making the battery "disappear" from the user's sight. Avoid users paying attention to the battery as much as they pay attention to the function of the device.

　　Choosing Battery Chemistry

　　The mutual constraints between batteries and systems are often overlooked issues in product design. It is critical to ensure that the battery capacity matches the system requirements. The most commonly used battery types for portable electronic devices are: alkaline batteries, nickel metal hydride batteries (NiMH) and lithium ion (Li+) batteries. They are not interchangeable, and most products have a best choice.

　　Disposable batteries: Alkaline batteries

　　Alkaline batteries are not rechargeable (a fact that has been emphasized repeatedly in recent evening TV commercials), but they have certain advantages due to their extremely low self-discharge rate and cost (they do not require a charger or AC outlet). For lower power applications, alkaline batteries will be a good choice, but to use these batteries properly, the quiescent current or sleep current must be low.

　　A common design mistake is to focus only on operating efficiency and ignore the current consumption in the "off" or "sleep" state. Even a few tens of microamps of current will consume battery power, so even intermittent operation of the product will lead to frequent battery replacement. Unfortunately, this design mistake is more common than it was a few years ago because many designs now use soft switches instead of mechanical switches (mechanical switches can completely disconnect the battery).

　　Rechargeable batteries: NiMH and Li+

　　When the load is too large for alkaline batteries or when frequent battery replacement is required, rechargeable batteries are a better choice, which has become the standard for portable products such as laptops, PDAs and cell phones. Rechargeable batteries should "disturb" users as little as possible and should promote the product (at least not affect product performance).

　　There are two common types of rechargeable batteries: NiMH batteries and Li+ batteries.

　　NiMH batteries cost less than Li+ batteries and can be chosen if the battery is safe for normal use in the product. This issue is more important for low-cost products that lack complex charging designs because NiMH batteries are suitable for the process of being fully charged and fully discharged. This is more suitable for products that often run out of power, such as power tools. However, a new type of NiMH battery with low self-discharge rate and negligible memory effect has recently appeared on the market, called "hybrid NiMH battery", and its representative brands include SANYO® Eneloop, Uniross® Hybrio®, etc. This type of NiMH battery retains its charge longer than traditional NiMH batteries, and generally only loses 15% of its charge in a year. The low self-discharge rate makes hybrid NiMH batteries very suitable for replacing alkaline batteries in applications where the battery is removed from the device after it is exhausted and recharged with an external charger. Such applications are common in digital cameras, but still require user intervention.

　　Many portable products are different from the above situation. PDAs and cell phones need to be charged regularly, but they only consume power occasionally. Li+ batteries are best used for these products. In addition to a good power-to-weight ratio, Li+ batteries have two important advantages: low self-discharge rate and no restrictions on short-term charge-discharge. Consumers do not have to consider "battery management" issues and rarely consider batteries during use, simplifying product use. Li+ batteries are particularly suitable for products with batteries that cannot be replaced by consumers.