By Alix Paultre, contributing editor

One of the most discussed and stressed-over
aspects of the latest revolution in portable, worn, autonomous, and remote
electronics is the battery. The problem is that people pay both too much and
not enough attention to it. They pay too much to the size, and less to the
need, the capability, and the functionality.

Design engineers understand the importance of
selecting the most optimized solution for their application, especially when
the device has demanding power requirements. Selecting the right battery
solution will directly affect the performance of the device and the experience
for the end user. Understanding battery chemistry and cell selection as well as
battery management systems will guide the proper battery selection and or
design.

Size: Does it matter?
When it comes to energy storage, does the size
of the battery matter? Actually, size isn’t as important as safety or
operational reliability, among other things. Pure power isn’t necessarily the
silver bullet to a design’s needs. It’s an easy out to address every range or
operating time issue by adding a bigger or supplemental battery, and a brisk
aftermarket in several application spaces exists to do just that. But it often
isn’t enough.

The issue is being able to provide the energy
that the system requires to fulfill the primary functionality for a reasonable
time at a price point both acceptable to the consumer and able to generate a
profit. However, in many cases, when designing a custom battery, size is a key
driver. With device manufacturers, battery requirements are often an
afterthought and an important component to ensuring that the design engineers
can provide a battery supporting the mechanical requirements in the form factor
that is needed.

We recently spoke to VARTA about the issues
facing engineers developing products and battery choice. Arkadiy Niyazov,
Project Manager at VARTA Microbattery, explained that for many engineers, it
isn’t battery capacity as much as it is form factor and functionality. Arkadiy
points out, “A custom battery pack often serves the customer better because it
allows for an optimal solution for not only the power requirement but also
safety and functionality.”

For example, in the rapidly-changing Li-ion
battery industry, the traditional 18650 cell size is not the only choice. New
options such as the 21700 and 26650 have now become more readily available,
providing design engineers with more choices to meet the form, fit, and
function needed to support the mechanical specifications of the end device
while still delivering the energy required by the system.

When it comes to energy management today, it often
isn’t how big the battery but how efficient the system it drives. In a
hypothetical case of two identical batteries in two nearly identical IoT
wearable medical systems, the one with better antenna matching will have a
significantly longer battery life than that of the system less elegantly
designed. Another example can be found in the coming wave of disruptive power
electronics based on wide-bandgap semiconductors, with not only higher
efficiencies but also higher power densities, smaller sizes, and reduced
cooling requirements.

Buy or build?
One of the most fundamental questions in
embedded design engineering is whether to procure subsystems off the shelf,
custom-made, or do-it-yourself. In the case of modular subsystems like
batteries, this can be a very difficult question to ask oneself. Not only are
standard battery sizes readily available, they are a mature interface that has
strong customer and industry support.

Providing a view from the field, Stefan Hald,
Field Applications Engineer (Power Pack Solutions) at VARTA said, “I see a lot
of requests from specialty spaces because they need to meet the
redundant electrical and thermal safety and protection demanded by the
application. The battery has to be as small as possible, but there also has to
be redundancy and monitoring functionality included. We are also seeing a lot
of requests for LED indicators for operational status, failure codes by
blinking, and the like.”

Consumer products with a relatively large form
factor have the hardest decision to make, as there is enough room to
accommodate a standard battery without concerns of packaging or size
compromises. This also applies to products that have evolved in form factors
that already have accommodated themselves to legacy battery adoption.

One way to sidestep the issue is to do both,
create a custom battery solution that also can work with off-the-shelf cells.
Companies with the assets to do so usually do it for maximum market penetration
while providing both an upgrade path for customers and an accessory sales
channel to support it. Video game controllers and cameras come to mind, both
high-use (high-power-drain) products with a customer base ranging from
entry-level newbie to passionate professional. This is obviously not possible
for every manufacturer, hence the difficulty of the decision.

On the “soft” side, multiple power options
benefit both the manufacturer and consumer for marketing and practical reasons.
Standard batteries are often the default choice unless there are form-factor
concerns that preclude use of off-the-shelf batteries. Until recently, form-factor
issues were the primary reasons that manufacturers went with a custom solution.

Often, user acceptance and form factor go hand
in hand. A single thin removable battery appeals to the customer while also
providing form factor and internal functionality to the manufacturer. For
example, this 1,590-mAh VARTA EasyPack SLIM measures 5.2 mm max and has a CE
Marking, a UL 2054 Listing, and IEC62133 Edition 2 compliance. This kind of
solution is often the best of both worlds as it is a “standard custom” kind of
solution that multiple products from multiple vendors can share.

Packing in functionality
The advantages of an optimized battery
solution, however, can far outweigh the additional costs involved in designing
a custom power pack into your product. As Stefan over at VARTA pointed out, the
most popular add-on functionalities currently involve the battery itself, such
as fuel gauging and safety monitoring. However, the ability to add
functionality to a device by putting it in its battery pack lets designers
provide features in a novel way that allows easy binning, scalability, and
upgradability to the customer.

One of the biggest problems is the previously mentioned
aftermarket add-on batteries. Many of these off-brand over-the-counter
batteries have no security or safety technology integrated at all; there is
often no way to tell if a store-bought battery is a real one from the
manufacturer or just a tootsie roll wrapped in a label thrown together by
scammers.

There are many stories of counterfeit bad
batteries destroying products via agents from leaked acid to catastrophic
thermal runaway (a fancy way to say, “It caught fire”). The first benefit of a
custom pack is that you can add an RFID chip for inventory and counterfeit
detection, a battery-monitoring IC to watch the charge state and thermals, or
buy a chip that has both of those functionalities and more.

Once you open the battery pack to drop in a
chip, your horizons broaden significantly. That chip could be a simple safety
and security device, or it could be one of the new crops of IoT wireless ASICs,
or it could be a complete SOC that lets you tailor your entire product line by
the kind of battery pack it takes.

When designing a custom battery, design
engineers need to understand cell technology for an application based on what
is the best technical fit, which, in some cases, can have very demanding power
requirements. Additionally, understanding cell technology trends will directly
impact the direction for a particular design including availability of cells
and new cell sizes such as Li-ion 26650 and 21700. Choosing the appropriate BMS
is equally as important as they can have simple electronics to measure cell
voltage or more complex BMS that affects the battery life and performance as
well as ensuring safety.

Another example can be found in the area of
robotics. Fig. 1 shows a VARTA battery pack that was
created for a human robotics project that required advanced functionalities like
fuel gauging and safety monitoring. The design included
sophisticated casting to withstand the mechanical forces certification
according to UL, a custom cell holder for production assembly and cell
positioning, and highly customized PCM for electrical control, battery safety,
and performance. Robots must not only operate remotely, they must be able to
detect low-battery situations accurately and quickly enough to address them in
real time either by reducing power needs or returning to base for recharge.

0418_Special_Power-Devices-2_Fig-1

Fig. 1: This VARTA battery pack was created for a human robotics project.

Wireless functionality
The aforementioned wireless functionality can
be implemented in many ways. Just integrating a cheap paper RFID tag in the
label would go a long way toward reducing counterfeit risks as well as
providing users with product information like pack capacity and may even give
the device being powered a rudimentary interface to first-level battery
functions like amount of charge and temperature.

In areas where there are options for the user
such as near-field communication (NFC) payments, it is possible to add regional
functionality to a device via the battery to address local or proprietary
communication protocols. Many places are now accepting NFC pay, but some manufacturers may not wish to deploy that
functionality across their entire product line. This also applies to internal
security devices for internal company resources that may vary from location and
facility.

The other major wireless functionality is
wireless charging. Once thought of for longer-ranged applications, wireless
charging is rapidly becoming a final-inch solution to eliminating batteries.
Adding independent wireless-charging capability to your product’s battery pack
delivers multiple benefits. Not only does this enable the user to buy multiple
battery packs and charge the unused packs with the same wireless power
interface, it allows the manufacturer to offer users of popular legacy products
an upgrade path to wireless charging.

Optical functionality
When one thinks of batteries, lights usually
come into the situation as loads. More often today, that light is an internal
LED showing charge state. In the future, that LED could also transmit optical
data, from troubleshooting information to augmented reality codes that would
let users fight virtual dragons emanating from the back of their phones.

These embedded LEDs (or in the future,
possibly OLED coatings) can also be used for aesthetic purposes as well as practical,
or both. Status LEDs could be made to blink in time with music or other data
(gaming) to enhance the smart-device experience, for example. The key is that
once you open the box to adding a light, there is nothing restricting you to
only one function for it, especially because most additional functionality can
be added in code.

Looking forward

Electronic engineers
have more and more choice when designing and specifying their battery packs,
with more options for security and functionality than ever before.
Understanding all of them (work with your supplier!) will help you greatly in
achieving your product design goals.