Reasonable choice of battery

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

In addition to their particular importance, the interplay of these features can enhance or diminish the end user's perception of the device. Generally, when users start to notice the battery, things get tricky! Good product design neither requires frequent battery replacement (such as a TV remote control) nor requires frequent recharging (electric toothbrushes), making the battery "disappear" from the user's sight. Avoid users paying as much attention to the battery as to the device's functionality.

Choosing Battery Chemistry

The mutual constraints between the battery and the system are often overlooked in the design. It is very important to ensure that the battery capacity matches the system requirements. Common battery types are: alkaline batteries, nickel metal hydride batteries (NiMH) and lithium-ion batteries. They are not interchangeable, and most products have an optimal choice.

Alkaline batteries

Alkaline batteries are not rechargeable (a point that has been emphasized repeatedly in recent nightly battery ads), but they have extremely low self-discharge rates and cost (no charger or AC outlet required). For lower power applications, alkaline batteries will be a good choice, but they must be used properly and the quiescent 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 if the current consumption from the battery is tens of μA, it will lead to frequent battery replacement. Now, many designs use soft switches instead of mechanical switches (mechanical switches can completely disconnect the battery), but this design mistake is more common than it was a few years ago.

Rechargeable battery

When the load is too large for alkaline batteries, rechargeable batteries are used, which has become the standard for portable products such as notebook computers, PDAs and cell phones. Rechargeable batteries should "intrude" the user as little as possible, promote the product, or at least not degrade the product's performance.

There are two rechargeable battery options: NiMH or Li-ion.

NiMH batteries cost less than lithium-ion batteries, and this choice becomes sensitive when the normal use conditions of the product are unsafe for the battery. This issue is more important for low-cost products that lack complex charging designs because NiMH batteries are suitable for the process of fully charging and fully discharging. This is more suitable for products that often completely drain the battery, such as power tools.

Another application where NiMH batteries are suitable is as a replacement for alkaline batteries, where the battery is removed from the device when it is depleted and then recharged by an external charger. This application is common in digital cameras, but requires frequent 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. These products are best to use lithium-ion batteries. In addition to weight density, this battery has two important advantages: low self-discharge rate and no restrictions on short-term charge-discharge. Consumers do not have to consider "battery management" issues, which simplifies product use.