Public Safety Advocate: Batteries in the Field

When we add smartphones and tablets to the mix of public safety communications devices we are adding yet another set of devices that run on batteries that need to be recharged. While there are a number of companies working on charging these devices from the radio energy that is transmitted from a cell site, which could make recharging a non-issue, that appears, once again, to be well into the future. In the meantime, how are these devices to be charged along with the Land Mobile Radio (LMR) handheld radios?

Comparing LMR to LTE Devices

LMR devices are generally designed for battery life of over a shift, which is ten hours or so. But this is with a duty cycle that is generally light. The norm is 80-percent standby (lowest power requirement) to 10-percent receive (mid-power requirement) and 10-percent transmit (highest power usage). The batteries for LMR radios are removable and replaceable and can be run through a “fast charge” system to replenish them in short order. There are also what are known as “clam-shell” battery cases that are designed to be used with disposable batteries, usually a number of AA cells. During major wildland fires when the forest services issue their cache of radios, they are mostly powered by throw-away cells. The batteries used in LMR radios are usually on the bottom of the radio, are easy to take off, and have a lot more battery capacity than batteries that are not removable.

There are a number of different scenarios for LMR radio distribution. In police departments, most LMR handhelds are staged in gang chargers and as patrol officers exit the station for a shift they will grab a radio and sometimes a spare battery for use on their shift and then replace the units in the charger at the end of their shift. In the fire service, since there are normally four assigned to an engine, radios are sometimes in chargers near one of the engine’s rear doors and are picked up as needed when arriving on a scene. Most EMS personnel have radios issued to them at the start of each shift. Of course, there are many variations of this including some departments where the LMR handheld is the only radio each person carries.

This was true in Cincinnati in the mid-1970s and when GE delivered its first order of GE PE handhelds they had nickel-cadmium batteries, which was the standard of the day. Ni-CADs, as they were called, developed a memory for each battery depending on the usage pattern. Therefore, patrol folks were happy with these new radios but the admin folks, who mostly kept their radio sitting in a desk charger, found that once they started to use the radio the battery life was measured in minutes and not hours! Needless to say, the battery engineers solved this problem in short order by introducing several different types of batteries.

LTE Device Batteries

Until the first iPhone hit the shelves at Apple and AT&T, most cell phones had removable and replaceable batteries and some had multiple-size batteries. Once the iPhone became the “standard” for all smartphones to follow, the removable/replaceable batteries went away. The battery technology and size of the battery in the smartphone was supposed to last more than a day of normal use. Then we started using smartphones almost constantly in our daily lives and I have to assume that it will, in many cases in the public safety world, be used for longer periods of time as well. Another difference is that LMR devices are in one of three modes: standby, receive, or transmit where smartphones are communicating with a cell site on a regular basis even in standby mode. This is necessary to determine which cell sector the phone is in so it can receive text and voice calls as they come in. Further, when most of today’s LTE phones are in the talk (transmit) mode they are also receiving. Add to this that having location services (GPS) on, Bluetooth on, and Wi-Fi on can also add drain to the battery. There are ways to minimize the battery drain but each of the services that is running does require power.

How many times have you recently traveled through airports and seen people charging their phones? How many of us own and use auxiliary battery packs to recharge our phone during the middle of the day? Have you ever forgotten to turn your phone to airplane mode when flying only to land and find your phone needs a recharge? Why? Because if a phone is on and cannot reach a cell site it keeps retrying until it is within range. LTE also adjusts the power level of the smartphone transmitter depending on how far the device is from the assigned cell site.

Charging in the Field

LMR radios are either not charged during an entire shift and then returned to a charger at the end of the shift or they are put into the charger at the end of every incident until the next one. But how are we to deal with smartphones in the field and how are we to make sure they are charged enough to be used when and where needed? My assumption is that as public safety becomes more familiar with FirstNet the devices will be used for more things such as dispatching calls using text, GPS for location, sending down building and hazardous area files, taking pictures and video to send back to the incident commander or operation center, receiving videos from a scene, and much more. There is a wild card here, too. If PTT over FirstNet is used on a regular basis there are some power issues, I am told, with PTT services staying “live” that may affect both power and network capacity issues during an incident.

Choices and Opportunities

Sonim is the company leading the charge to outfit public safety with smartphones with built-in PTT and are ruggedized as well. Sonim has two phones presently that permit swapping out batteries and it offers a number of different charger capabilities including rack chargers for multiple devices. So far as I have been able to determine, the other devices including those recently certified by NIST for FirstNet use, have battery-charging options for both multiple units, and mobile drop-in chargers for use in fire rigs.

Today, the choice of devices includes Samsung Galaxy S9 and S9+ with band 14 included in the device, the Sonim Technologies XP5S and XP8, seven Apple iPhones (none with band 14 included), the Samsung S8 series again with no band 14 access, the Apple iPad and iPad Pro, and the Netgear MR100-330 hot spot. I am sure this list will grow and it will be interesting to see how all the vendors handle the battery/recharging issue. I do not expect Apple or Samsung to suddenly add removable batteries to their consumer line of products but for administrative and other non-front-line personnel who have access to smartphone chargers during the day, the battery issues won’t be as critical as those on the front lines.

There have always been battery issues. Some departments are lax in replacing LMR radio batteries until they simply die, develop charging issues, and more. I suspect the addition of FirstNet devices will require some new battery management ideas and options. I also suspect that even though FirstNet is a small niche market, since the devices and technology are being deployed worldwide for public safety, there will be a number of battery advances and battery solutions coming to the market to assist in the issues discussed above.

Battery sizes vary, too. For example, in the two Sonim phones with removable batteries the batteries are available in either 1750 mAh (milli-Amp-hour) or 3180 mAh. Typical smartphones have battery capacities of 950 mAh or larger, and a Motorola APX LMR handheld sports batteries that are 1900 mAh and up to 4850 mAh. Of course, each larger battery is heavier and longer when attached to the radio. Many smartphones do not specify the size of the battery but use specs such as: talk time up to 21 hours, Internet use up to 12 hours, video playback up to 13 hours (iPhone 8). Seems like plenty of spare battery life but we do not really know all of the demands that will be placed on these devices as we learn more about how to “tune” FirstNet to the needs of the public safety community.


It is important for public safety to remember something every one of them already knows. This little guy named Murphy is sitting around waiting to throw a monkey-wrench into the works. The good news is that except for Apple devices, the rest of the smartphone devices have all settled on micro-USB connectors, usually on the bottom of the devices. This should be a help in getting charging devices into the market. We have forms of wireless charging now, using pads in vehicles and our homes and there are external charging packs. Battery technology is advancing but there are still issues and we have all faced them. When we need to make the day’s most important phone call, our battery is dead. A real inconvenience for the general public but just one more reason for LMR and LTE to live in harmony for years to come.

Andrew M. Seybold
©2018 Andrew Seybold, Inc.


1 Comment on "Public Safety Advocate: Batteries in the Field"

  1. Andy, I remember a few years back Metro-Dade Police had made the switch to Lithium-Ion Polymer (LiPo) batteries for their portable radios.This was after several incidents where officers had battery failures during critical situations late into their shift. Metro radio engineers had extensively tested the LiPo batteries and found the same size (and weight) battery with the LiPo chemistry lasted 60-80 % longer that a comparabile Lithium Ion battery pack and a very low self discharge rate. At the time it seemed like these cells would overtake Lithium-Ion in a very short time but I’m only aware of these being offered by after market companies today.

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