Section 6.2: Batteries and Power Systems #

You covered battery basics when studying for your Technician license—the different chemistries, safety around shorting and overcharging, calculating runtime from amp-hours. Now let’s dig into some specifics that matter as you expand your operating horizons: keeping lead-acid batteries healthy, choosing batteries that can handle transmit current, powering mobile stations properly, and safely integrating solar charging.

Lead-Acid Batteries: Cheap and Easy #

Lead-acid batteries have been around forever, and there’s a reason they’re still popular: they’re inexpensive, are generally still usable at cold temperatures, widely available, and you can often find used ones that still have plenty of life left. They’re not the lightest or most elegant solution, but when you need a lot of amp-hours without spending a lot of dollars, lead-acid delivers.

The Voltage Floor #

Every battery chemistry has a point of no return—discharge below it, and you cause permanent damage. For lead-acid, going too deep causes sulfation, where crystals form on the plates and steal capacity you’ll never get back.

Key Information: The minimum allowable discharge voltage for maximum life of a standard 12-volt lead-acid battery is 10.5 volts.

Here’s the gotcha: voltage sags under load. Your battery might read a comfortable 12.2 volts while you’re listening, then drop below 10.5 volts the moment you key up to transmit. If you’re serious about battery longevity, monitor voltage while transmitting—or better yet, use a low-voltage cutoff that protects the battery automatically. Your future self (and wallet) will thank you.

Internal Resistance: The Hidden Spec #

Ever wonder why two batteries with the same amp-hour rating perform so differently? The secret is internal resistance—opposition to current flow inside the battery itself.

Key Information: An advantage of batteries with low internal resistance is high discharge current.

When your transmitter demands 20+ amps, internal resistance determines whether the battery delivers or disappoints. If there is a high internal resistance, the voltage will drop significantly under load, potentially causing your transmitter to shut down or perform poorly. Look for batteries marketed as “low internal resistance” or “high discharge rate” to ensure reliable performance during transmission.

Car starting batteries have very low internal resistance—they’re designed to crank hundreds of amps to your starter motor. They are also generally expected to remain mostly charged all the time—they hate deep discharge; run one down repeatedly and you will rapidly decrease its lifespan. Deep-cycle batteries tolerate repeated cycling but often have higher resistance. AGM (Absorbed Glass Mat) batteries split the difference nicely for ham radio use—low enough resistance for solid transmit performance, robust enough for regular cycling.

Lithium Batteries: A Growing Standard #

LiFePO4 (lithium iron phosphate) batteries have gone from exotic to nearly mainstream in recent years, and for good reason. They’re roughly half the weight of lead-acid for the same capacity, deliver more usable amp-hours (you can safely use 80% of their capacity versus maybe 50% for lead-acid), and last for thousands of charge cycles. Yes, they cost more upfront—but when you factor in lifespan and performance, they often win on value too.

The trade-off? They’re pickier about charging, which we’ll cover when we get to solar systems.

Mobile Power: Doing It Right #

Working HF from your vehicle is one of the great joys of General privileges. But a 100-watt transceiver pulling 20+ amps on voice peaks needs more than a casual power connection.

Go Straight to the Source #

For serious mobile power, there’s really only one right answer.

Key Information: The best direct, fused power connection for a 100-watt HF mobile installation is to the battery using heavy-gauge wire.

Direct battery connections bypass all the electrical noise from your vehicle’s computers, fuel injection, and other electronics. For best results, use at least 12 AWG wire (10 AWG would be better) with a fuses on both leads to the battery. Yes, it’s more work than tapping into an existing circuit, but the existing circuits weren’t designed to handle the load or noise sensitivity of HF operation.

That Tempting Cigarette Lighter Socket #

It’s right there. It’s already wired. It even has a convenient plug…

Key Information: DC power for a 100-watt HF transceiver should not be supplied by a vehicle’s auxiliary power socket because the socket’s wiring may be inadequate for the current drawn by the transceiver.

Vehicle manufacturers wire these sockets for phone chargers, not transceivers. Thin wire, small fuses, and connectors that weren’t designed for 20+ amps add up to trouble. Best case: you blow fuses at inconvenient times. Worst case: wiring quietly overheats somewhere behind your dashboard. Don’t do it.

Solar Charging #

Solar panels and ham radio go together beautifully—silent power for Field Day, keeping batteries topped up at a remote site, or just reducing your dependence on the grid. But a few details matter.

When Darkness Falls #

Here’s something that’s easy to overlook: solar panels don’t just stop generating power at night—they actually become a small load that slowly drains your battery backward through the cells.

Key Information: A series diode should be connected between a solar panel and a storage battery that is being charged by the panel to prevent discharge of the battery through the panel during times of low or no illumination.

A blocking diode acts like a one-way valve, letting current flow into the battery while preventing it from sneaking back out overnight. Simple problem, simple solution. The most common solution to this is to just use a “Solar Charge Controller”, which also handles regulating the charge voltage and current to the battery.

Lithium Batteries Need a Chaperone #

Remember how we said LiFePO4 batteries are pickier about charging? Here’s where that matters.

Key Information: When connecting a solar panel to a lithium iron phosphate battery, the solar panel must have a charge controller.

While it’s often a good idea to use a charge controller with any battery, Lead-acid batteries are relatively forgiving—overcharge them a bit and they’ll probably still be okay. Lithium cells don’t have that tolerance. Overcharge them and you risk damage to expensive batteries or, in extreme cases, safety hazards. A charge controller regulates voltage and current to keep everything happy. This isn’t optional equipment—it’s required for safe operation. Most often a Lithium battery will also have a “Battery Management System” (BMS) built in or added on to handle cell balancing and additional safety features.

Lithium batteries also quickly degrade in performance at low temperatures. Make sure you know the temperature limits of your battery and charge controller, and avoid using them in conditions that exceed those limits.

Generator Safety #

When the sun isn’t shining and the batteries are low, generators save the day—but like everything else, they come with safety considerations.

Carbon Monoxide: The Silent Threat #

Generator exhaust contains carbon monoxide—colorless, odorless, and deadly. You can’t smell it, you can’t see it, and by the time you feel symptoms, you may be too confused to save yourself.

Key Information: An emergency generator installation should operate in a well-ventilated area.

“Well-ventilated” means outdoors. Not in the garage with the door cracked. Not under the carport. Outside, at least 20 feet from buildings, with exhaust pointed away from any doors, windows, or air intakes. Carbon monoxide is heavier than air and loves to pool in low spots and seep through cracks. Don’t give it the chance.

While we’re on generator safety: let the engine cool before refueling (hot exhaust plus gasoline vapors is a bad combination), and never backfeed house circuits without a proper transfer switch—you could electrocute utility workers trying to restore power to your neighborhood, which is what we in the hobby usually refer to as a Bad Thing™.

Soldering Safety #

Building and repairing equipment is part of the fun, and that usually means soldering. Traditional electronics solder contains lead, which requires a few simple precautions.

Key Information: Lead can contaminate food if hands are not washed carefully after handling the solder, which is a danger from lead-tin solder.

Lead accumulates in your body over time, so the issue isn’t one soldering session—it’s years of careless habits. The fix is simple: wash your hands thoroughly after soldering, and don’t snack at your workbench. Keep your soldering area ventilated to avoid breathing flux fumes. Lead-free solder works well for most projects if you’d rather avoid the concern entirely.

Whether you’re running on batteries, solar, generator, or wall power, all that energy needs somewhere safe to go when things go wrong. That’s where grounding comes in—and as we’ll see in the next section, “grounding” means several different things depending on whether you’re worried about lightning, RF, or electrical safety.