The following article originally appeared in the April 2021 issue of The Spectrum Monitor magazine:
I’ll admit it: I’m a massive fan of field radio.
In 2020, I easily spent a total of 100 hours outdoors with my radios activating a total of 82 sites for the Parks On The Air (POTA) program alone. This doesn’t include hours and hours of SWLing (shortwave radio listening). It’s been great.
Taking radios into the field is so much easier to do today than it was in, say, 1985 or earlier, because we have so many more options for powering our gear in the field. Not only have radios become more efficient in operating off of battery power, but we now have so many affordable and lightweight rechargeable battery choices on the market.
In the following article, let’s take a look at some portable battery power options for your radio gear. By “portable,” I’m talking power options for those of us who load a backpack or carry case and head to the field.
To keep the scope of this article in check, I’m also going to focus only on rechargeable battery options. And rather than get bogged down in the nuances of battery chemistries, we’ll focus on the end result––the pros and cons of each battery type, and how practical they might be for your field application.
In addition, I’ll also limit discussion to batteries that can be purchased of-the-shelf rather than addressing homebrew options. While I love building things, I’m very cautious when dealing with battery charging because if not done correctly, the results can be dangerous. I prefer obtaining products from trusted suppliers who thoroughly engineer and test their equipment.
Let’s take a look at several types of batteries, and speak to their advantages…as well as disadvantages. Then––as we summarize our findings––let’s discuss how to choose the right option for your needs.
Consumer-grade rechargeable batteries
Let’s begin by talking about the lowest-hanging fruit in terms of portable power: everyday rechargeables in the form of 9V, AA, AAA, C, and D cells.
While, admittedly, these batteries are not typically an option because of their limited capacity and energy density, they can still be a very practical power source for portable receivers and even a few QRP transceivers.
Rechargeable battery chemistries have improved with time, thus I no longer purchase nickel-cadmium (Ni-Cd or NiCad) or legacy nickel metal hydride (NiMH or Ni–MH) batteries.
These days I almost exclusively purchase low-self-discharge nickel metal hydride (LSD NiMH) batteries, specifically, Panasonic Eneloop batteries (Amazon affiliate link). Although they’re a pricey option compared with generic NiMH batteries, and might even be overkill for certain applications, I do love the shelf life of Eneloops.
Of course, the benefit here is Eneloops have that low self-discharge. They will maintain charge better at rest (i.e., when not in use) than legacy NiMH or NiCad batteries. From my real-word usage, I’m convinced that Eneloops also demonstrate better longevity over numerous charge/discharge cycles than many others.
All of my portable shortwave receivers that accept AA or AAA batteries are powered by Eneloops exclusively.
And although I’ve never done this myself, it is also possible to power highly-efficient QRP transceivers with Eneloop batteries, so long as you use a multiple battery holder to increase voltage and capacity to match both your rig and your desired amount of operating time.
Keep in mind, though, that most transceivers will require a block of at least ten AA batteries to reach a voltage around 12 VDC. As you might imagine, it can be cumbersome after using your radio in the field to remove all ten of these batteries and charge them in a charger that can only hold, say, four batteries at a time. I personally prefer other options, but this one is certainly a fairly affordable, safe, and accessible option.
Note that in recent years, Panasonic started offering Eneloop Pros: while pricier than standard Eneloop batteries, they offer slightly higher capacity at the expense of overall longevity (roughly 500 versus 2100 total charge/discharge cycles). Since the voltage is the same, I’ve never felt the need to use higher-capacity Eneloop Pros.
Rechargeable Panasonic Eneloop AA batteries (non-Pro version):
- Price: $2.25 – $4 US per battery, depending on the number in the package
- Weight: 4 grams/.4 ounces per cell
- Voltage: 1.2 V each
- Longevity: Excellent, up to 2100 charge/discharge cycles
- Ease of recharging: Simple via Eneloop OEM chargers
- Solar- charging option: Eneloop originally marketed solar chargers, but doesn’t seem to do so presently
Sealed Lead Acid (SLA) Batteries
When I first became a licensed ham radio operator in the late 1990s, sealed lead acid batteries were the primary battery power source used for field radio operation.
At the time, these batteries were one of the best options for portable radio use because they could be purchased in a variety of sizes (based on amp hour capacity), and unlike flooded lead acid batteries, they required no maintenance––and being sealed, did not outgas.
While I’ve owned everything from 3 Ah to 15 Ah SLA batteries, I found the once-ubiquitous 7-8 Ah size to be the “sweet spot” in terms of portability and capacity.
SLA batteries are still among the most accessible high-capacity batteries on the planet. No matter where you travel, it’s likely you’ll be able to hunt them down in any hardware or electronics store. Our small local hardware store has a wide selection of these at their battery kiosk.
What are some of the pros of these batteries? In terms of “bang for buck,” the SLA is still hard to beat. You can purchase a quality 7.2 Ah 12-volt SLA battery for about $18-20 US (affiliate link). This would be more than enough battery to power a typical QRP transceiver for many hours on end. Chargers are also inexpensive––you can purchase a dedicated charger for about $10-15 US. Not bad.
In addition, 12-volt batteries are nearly ideal for amateur radio use since most transceivers are designed to operate with 12-13.8 volts DC +/- a modest margin.
There are some negatives compared with more modern battery chemistries, however. For one, SLA batteries are much heavier than the batteries we’ll discuss in the following sections. After all, they’re (still) made of lead! In addition, the battery’s longevity will be negatively impacted if you discharge it too deeply.
With that said, if you take care of an SLA battery, it can give you five or more years of service life in the field, yielding an excellent value for the modest investment. If you have an application that requires relatively little capacity from the battery, you might get a very long service life, indeed. In 2011, I built a remote antenna tuner box around an LDG Z11 Pro ATU and a discarded 7Ah 12V SLA battery. At the time, this battery could no longer hold voltage long enough to be reliable in the field, but I knew the Z11 Pro requires very little in the way of power, so I thought I’d try it as a power source anyway. Since the remote ATU box isn’t near an outlet, I charge the SLA battery with a 5-watt solar panel I purchased used at a hamfest with a Micro M+ charge controller. A decade has now passed, and that SLA battery continues to power the Z11 Pro even through seasonal temperature variances of -10F/-23C to 90F/32C. Not bad! Again, keep in mind this application works because the Z11 Pro is so flexible in terms of power requirements––it’ll operate on 6-16 volts DC at 300 mA with a 20 uA standby current.
Clearly, SLA batteries are affordable candidates for back-up power in the shack during occasional power outages.
- Price: Most affordable option per Ah of the batteries listed here
- Weight: By far, the heaviest of all the battery options in this article
- Voltage: Various, but 12VDC is very common
- Longevity: Very good if properly maintained
- Ease of recharging: Easy, via simple charge controllers
- Solar charging option: Multiple types of charge controllers can be used with SLA batteries; among the listed batteries, the easiest and least expensive to charge via solar
Without a doubt, lithium-ion batteries have revolutionized the consumer electronics world.
Why are they so popular?
First of all, their construction allows for a variety of form factors ranging from cylindrical cells to slim packs and pouches so thin they can fit in an ultra-thin mobile phone, eReader, or tablet. They’re the easiest type of battery to accommodate in compact consumer electronics, and indeed, they power most of the consumer electronics we’ve put to use in the last decade.
Secondly, they have a very high energy density, thus pack a lot of capacity for the size and weight. Indeed, if size and weight are your primary requirements, li-ion batteries should be high on your list.
In addition, Li-ion batteries are ubiquitous and affordable because they’re used in so very many applications.
There are negatives, though, with these power sources. First and foremost, they’re very sensitive to over-voltage and over-current events that initiate a thermal runaway. To prove this point, I’ll share some first-hand experience from the early days of large lithium-ion packs…
Li-ion Horror Story
In 2011, I evaluated a lithium-ion battery pack with integrated 5V USB chargers and even a simple one-outlet inverter from one of the big names in portable power systems. At the time, this was a new battery pack and a relatively new technology, at least in terms of the energy density and compact size. After receiving the battery, I charged and discharged it perhaps twice during testing. I had a flight scheduled from North Carolina to California, and decided I’d take it in my carry-on bag to power my laptop in flight. It worked fine on the flight to KSFO. Once there, I recharged it. On my return flight, it simply didn’t work. I thought perhaps I hadn’t plugged it in properly, or that the hotel outlet I used didn’t work. Upon arrival I emptied my travel pack onto the bed and plugged in the battery pack; it indicated it was taking a charge.
After doing a few projects around the house, I went back up to the bedroom and was greeted with an overpowering smell––almost like the pungent chemical odor of nail polish remover. I looked everywhere for the source of the odd smell. Finally, I located it: it seemed to be coming from the battery pack. Upon examination, I could tell the battery had begun to swell. As I lifted it up, I noticed that the bottom portion was essentially in a state of melting. As quickly as I could, I unplugged it and removed it from the room. I then discovered that in the thermal runaway process, it had begun burning through the sheets and mattress of the bed. Shocked, I suddenly realized it could have burned down my home.
Keep in mind, I was completely new to this battery technology, and this was years before thermal runaways made the news and airlines began restricting their transport. To my relief, the company from which I purchased the pack ended up pulling that model off the market, and even reimbursed me for the mattress and bedding. But it was a hard lesson learned.
If I’m being perfectly honest, this lesson had a major impact on my willingness to experiment with Li-ion battery packs.
The problem with the model of pack I had purchased was not the battery chemistry or construction, per se, but the charge controller). The fact is, Li-ion batteries require millivolt accuracy and a number of protections to detect and stop thermal runaway. Battery packs with multiple cells need a battery management system (BMS) that also balances the cells and monitors them closely. Fortunately, most manufacturers of the technology now understand this.
Modern Li-ion cells and chargers are much safer and more stable
Since then, Li-ion battery chargers have become both orders of magnitude safer and more effective. Still, I only charge these batteries on a surface which, should the battery be tempted to melt down, would be less likely to be damaged or serve as a fire hazard. I also never leave them unattended during charging.
With that said, I don’t think Li-ion batteries are to be feared. Obviously, many of us walk around with one tucked in our pocket all day––in our smartphones! They’re generally considered very safe now. Of course, I’d only buy the best and would steer away from the lowest-costs units you might find on eBay and Aliexpress, as many of these products are made in places with little oversight or regulation.
Another interesting fact about Li-ion battery packs is that since their voltages are usually available in multiples of approximately 3.6 volts (e.g., 3.6, 7.2, 10.8, 14.4 and 18 volts), they are not always ideally suited for radios that require 13.8V input power. Some packs, however, have circuitry that provides an output voltage closer to your desired amount.
One Lithium-ion battery pack I’ve been using with my Mountain Topper MTR-3B, Elecraft KX2 and KX3 transceivers is a (very affordable) TalentCell rechargeable 3000 mAh Li-ion battery pack that provides both 12V and 5V USB power. It has built-in charging circuitry and is very compact. I purchased mine for about $25 on Amazon.com, and have been very pleased with it so far.
Summits On The Air operators often place priority on smaller-sized and lighter-weight power sources, and thus turn to Li-ion battery packs. Many SOTA friends have invested in high-quality balance charger/dischargers to maximize the life of their batteries, and have been happy with the performance they receive. A quality charger may costs upwards of $60, but is worth the investment if you choose Li-ion batteries as your portable power of choice.
- Price: From affordable to pricey, depending on capacity and charger investment
- Weight: The lightest weight portable battery options in this list
- Voltage: Often in multiples of approximately 3.6 volts: (3.6, 7.2, 10.8, 14.4 and 18VDC)
- Longevity: Good. Typically around 400-500 charge cycles if properly maintained
- Ease of recharging: Simple, if a self-contained pack; more complex, if using multiple cells that need balancing
- Solar charging option: Not advised (yet). There are a number of homebrew Li-ion solar charging projects on the web, but I believe this battery chemistry fares better with a balance charger connected to a stable AC power supply.
Lithium Iron Phosphate (LiFePo4/LFP)
The final type of battery chemistry we’ll cover here is my favorite of the bunch.
There are good reasons why Lithium Iron Phosphate batteries have become one of the choice rechargeable batteries for field radio use.
- LiFePo batteries are inherently stable and safe
- They offer a longer cycle life than that of other Li-ion, NiMH, NiCad, or Lead Acid batteries–thousands of charge cycles as opposed to hundreds
- LiFePO batteries have an excellent constant discharge voltage
- LiFePo batteries use phosphates––as opposed to cobalt or nickel, which are supply-constrained and carry heavier environmental concerns
- LiFePo batteries have a lower self-discharge
- LiFePo batteries are very lightweight compared to SLA batteries
- 3.2 V nominal output voltage means that four cells can be placed in series for a nominal voltage of 12.8 V, near ideal for most field radio gear
Any cons? Yes…while they’re lightweight, LiFePo4 batteries aren’t as compact as Li-ion battery packs. But the primary negative here is the price. At time of print, LiFePo4 batteries have the highest cost per Amp hour of the batteries discussed in this article. With that said, due to the excellent longevity of these batteries, the LiFePo may be the most cost effective option in the long term.
LiFePo4 battery systems sport built-in battery protection modules to address concerns like over-voltage and balancing.
How do LiFePo batteries stack up?
- Price: One of the pricier options, when you include the battery and charger
- Weight: Very light weight, but size tends to be larger than comparable Li-ion packs
- Voltage: Excellent match for gear requiring 12V – 13.8 VDC
- Longevity: Excellent. Thousands of charge/discharge cycles
- Ease of recharging: Simple, using the provided charger (battery packs have a built-in charge controller)
- Solar charging option: Bioenno sells charge controllers designed to work with LiFePo batteries, handy for the field
Without a doubt, the best-known LiFePo battery manufacturer in the world of ham radio is Bioenno Power. I’ve purchased their batteries exclusively and have been incredibly pleased with the quality, longevity, and performance of their products.
Choosing the right battery for you
Each one of these battery types have their pros and cons, and you can find lengthy, in-depth discussions online about the nuances of each battery chemistry. At the end of the day, however, what matters is which one best suits your particular application and provides your gear with the appropriate amount of voltage.
Here’s when I would reach for each of our types of batteries…
NiMH LSD AA batteries
If you’re willing to use a battery pack to run 8-12 cells in series to achieve your required nominal output voltage, Eneloop batteries are relatively affordable, lightweight, and of course, power an array of electronic devices in our world.
If you plan to use QRP power for short periods of time, these may suit your needs quite well. My buddy and Elmer, Eric (WD8RIF), has used Eneloop batteries to power his Elecraft KX3 for the majority of his Parks On The Air activations.
Of course, AA Eneloop batteries are also invaluable for those of us who have an arsenal of portable shortwave radios that accept AA cells!
Sealed Lead Acid Batteries
If you’re on a very tight budget and weight is less of a concern, SLA batteries are a great choice. They’re an especially affordable option if you plan to make a solar-powered battery pack since charge controllers are quite simple and affordable.
If you’re looking for a stationary back-up battery for home, these are an excellent choice, as long as you keep the charge topped up.
Backpacking or flying overseas, and size and weight really do matter? Purchase a Li-ion battery system. Li-ion cells and packs offer the highest energy density of any of the battery chemistries in this list. They’re incredibly compact––and as long as you use a quality charge controller with built-in protections, and you don’t damage or puncture an actual Li-ion pack––they should be quite safe, and you’ll be pleased with performance. Note: Keep in mind some airlines have regulations about the size of Li-ion battery pack you’ll be allowed to carry on board, so do check before departure.
If you’re looking for a simple, effective portable battery solution that is almost custom-designed to power radio gear, invest in a LiFePo4 battery and charger. I have everything from a 15 Ah 12V LiFePo4 battery that can power my 50 watt Mission RGO One transceiver, to a 3 Ah 12V pack I now use for 2-3 hours in the field at a time with my QRP transceivers. Bioenno has recently sent me a 9 V 3 Ah battery pack to test with my Mountain Topper MTR-3B––it’s incredibly compact, since it only needs three 3.2V cells in series. LiFePo batteries are also the ones I suggest for those who are new to the world of battery packs and want something that is hassle-free and simply performs.
I admit, I’m being transparent here about why I own a total of three LiFePo4 batteries from Bioenno Energy––they’re amazing and I know I can rely on them.
…I would offer this final piece of battery-usage advice: whatever you do, don’t “cheap out” on your battery and charging system. No matter what chemistry you decide to purchase, buy the best quality you can afford. If using any variant of a Li-ion battery, heed my tale, and be sure any separate charge controllers you employ will protect your battery (and your home)!
And now…Go out there and have fun. I assure you: when you take your radios––whether portable shortwave radios or ham radio transceivers––to the field, you’ll find you can escape all of the noises that so often plague us indoors. And out there, you, too, may find your radio bliss.