Battery Power for the Small-Space Shack: What LiFePO4 Actually Fixes
How a 12V LiFePO4 battery replaces a switching supply in a restricted-space shack: the noise floor it buys, the runtime math, and the charging habit that undoes both.
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The noise floor article on this site names switching power supplies as one of the two or three most common indoor RFI sources, right next to LED drivers and powerline networking adapters. The fix it offers for a laptop charger is "ferrite, or run on battery while operating." That second option deserves its own treatment, because it applies to more than laptops. It applies to the radio itself.
Why the switcher is the problem in the first place
A switching power supply generates 13.8V for your radio by chopping the AC mains at tens or hundreds of kilohertz and filtering the result back down to DC. That chopping frequency and its harmonics do not stay contained inside the supply. Some of it rides out on the DC leads to your radio, some of it radiates directly from the supply's case and transformer, and in a small space the distance between the supply and your antenna feed point is often a few feet, not a few rooms. The harmonics of a 65 kHz switching frequency land all over 80m, 40m, and 20m. That is the mechanism, not a coincidence: any switcher close enough to couple into your feedline or your equipment ground is a candidate noise source, and small spaces put everything close together by definition.
A linear supply does not have this problem because it does not switch. It drops AC to DC through a transformer and a linear regulator, both of which operate at 60 Hz, well below anything that shows up as HF noise. A battery does not have this problem either, for the more obvious reason that it is not converting anything. Twelve volts DC in, twelve volts DC out, no chopping frequency to radiate.
What a battery buys you that a linear supply does not
Both a linear supply and a battery solve the conducted-noise problem. Only the battery solves two others.
No mains connection at all. A battery-powered station has no AC cord running to the operating position, which matters in an attic, a closet, or a balcony corner where there is no outlet and running an extension cord raises its own set of problems, covered from the antenna side in the attic antenna article. Portable-by-necessity spaces get a full HF station without a wiring project.
No current draw on a shared circuit. The indoor QRP reality article covers the electrical math: a QRP transceiver at 5W draws 2 to 3 amps from a 13.8V source, and the AC-side draw from a linear or switching supply feeding that load is small but nonzero. A battery draws nothing from the wall. In a building where your 15-amp circuit already carries a computer, a monitor, and whatever your neighbor's unit shares the breaker with, that is one less variable during a long digital-mode session.
Neither of these is a noise-floor argument. They are a where-can-you-operate argument, and in a restricted space that argument often matters as much as the RFI one.
Sizing the pack to the radio
Amp-hour math is straightforward once you have the current draw, and the QRP article already supplies it. A QRP rig at 5 watts pulls roughly 2 to 3 amps on transmit and a fraction of an amp on receive. A 6Ah LiFePO4 pack, divided by a worst-case 2.5A continuous key-down draw, gives about 2.4 hours of theoretical full-power transmit time. Real operating time runs longer than that math suggests, because SSB duty cycle sits around 30 to 40 percent and FT8's 15-second transmit slots average out lower still across a full session. A 6Ah pack is a realistic all-afternoon battery for QRP digital modes and a solid multi-hour battery for QRP voice.
A rig running the higher end of "QRP-adjacent" power, like a Xiegu G90 dialed down from its 20W ceiling, draws more current and eats into that runtime faster. Match the pack to the rig you actually run, not the rig you might someday run.
Two packs that fit a small-space station
| Pack | Capacity | Chemistry | Weight | Notes |
|---|---|---|---|---|
| Bioenno Power BLF-1206A | 12V, 6Ah | LiFePO4 | Under 2 lbs | PVC case, integrated protection circuit, battery only, charger sold separately |
| Talentcell LF4011 | 12.8V, 6Ah (76.8Wh) | LiFePO4 | Under 2 lbs | Rated 2000 charge cycles, DC output |
Both are 6Ah at 12V-class output, both are LiFePO4 rather than lithium-ion, which matters for the same reason it matters in any small enclosed space: LiFePO4 is chemically far more resistant to thermal runaway than the lithium-ion cells in a laptop or phone pack, and a battery sitting next to your operating position for hours at a time is not somewhere you want to introduce that risk. Check the connector each pack ships with before you buy. Neither arrives wired for Anderson Powerpole out of the box, and Powerpole is the connector standard the rest of the portable ham radio world uses, so budget for a crimp set or a pre-made adapter cable.
The case for staying plugged in
A battery is not automatically the right answer. If your station lives at a fixed desk with mains power available and portability is not the point, a linear supply gets you the same conducted-noise benefit without the recharge cycle to manage. The Astron RS-35A is the reference example in the hobby, a 25A-continuous linear supply that has been the default recommendation for a fixed HF station for decades precisely because it does not inject switching noise into a shack that is already fighting for a clean noise floor.
Astron RS-35A Linear Power Supply on Amazon
The trade-off is size and weight. A linear supply rated for 100W HF operation is a dense, heavy box built around an equally heavy transformer, nothing you carry to a balcony session or store in a closet between uses. For a permanent indoor install where the antenna and the operating position do not move, that trade-off is a good one. For anything that needs to set up and pack away, it is not, and the Field Day from an apartment article covers what that packable version of the station looks like end to end.
The charging trap
Here is the mechanism that undoes the entire point if you miss it. Most compact LiFePO4 chargers, including the ones sold alongside packs like the two above, are themselves small switching supplies. Charge the battery while you are operating and you have reconnected a switcher to your power system, with an extra battery in between it and the radio. The noise floor gain evaporates for as long as the charger stays plugged in.
The fix is a habit, not a purchase: charge between sessions, not during them. Top the pack off after you shut the station down, disconnect the charger before the next session starts, and the battery runs the radio on pure DC with nothing upstream generating harmonics. This is the same logic the noise floor article applies to a laptop, phrased as "run on battery while operating." The battery is the operating state. The charger is a separate state that should never overlap with it.
The bottom line
A switching supply a few feet from a compromise antenna is a measurable, well-understood noise source, and a LiFePO4 battery removes it entirely by removing the conversion step that causes it. A 6Ah pack sized against your rig's actual current draw covers a realistic operating session, runs anywhere with no outlet requirement, and adds nothing to a shared circuit's load. A linear supply buys the same noise benefit for a station that never moves and never needs to be disconnected from the wall. Pick based on whether your station is fixed or portable, not on which one sounds more capable, and keep the charger off the bench while the radio is on.