Batteries and Power Cells

A battery converts stored chemical energy into electrical energy. For ham radio operators, batteries are not just a convenience — they are critical infrastructure for portable, mobile, and emergency communication. Understanding battery chemistry, capacity, and discharge behavior allows you to choose the right battery for the job and keep it working reliably when it matters most.

How Batteries Work

A battery cell contains two electrodes — an anode (negative) and a cathode (positive) — separated by an electrolyte. A chemical reaction at each electrode produces or consumes electrons. The anode releases electrons into the external circuit; the cathode accepts them. This flow of electrons through the external circuit is electric current.

A primary battery undergoes a non-reversible chemical reaction — once the chemicals are consumed, the battery is discharged and discarded. A secondary battery (rechargeable) uses a reversible reaction: applying current in the reverse direction regenerates the chemical reactants, restoring the battery to its charged state.

A battery pack is formed by combining multiple cells. Cells in series add their voltages; cells in parallel add their capacities. A 12 V lead-acid battery, for example, contains six 2 V cells wired in series.

Battery Chemistries

Different chemical systems offer different combinations of voltage, energy density, cycle life, self-discharge rate, and cost. The right chemistry depends on how a battery will be used.

Typical discharge curves for common battery chemistries. LiFePO4 and SLA maintain a relatively flat voltage during discharge; alkaline voltage drops steadily; NiMH has a flat plateau before a sharp drop.

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Alkaline (Primary)

Alkaline cells (AA, AAA, C, D, 9 V) are inexpensive, widely available, and have a low self-discharge rate — they retain most of their charge for 5–10 years in storage. Nominal cell voltage is 1.5 V, dropping gradually as the cell discharges. Alkaline cells are suitable for low-to-moderate current loads; high current draws cause the voltage to sag significantly. They are common in handheld radio battery packs as an emergency backup option.

Nickel-Metal Hydride (NiMH, Rechargeable)

NiMH cells have a nominal voltage of 1.2 V and typical capacities from 600 mAh (AAA) to 3000 mAh (AA). They are rechargeable for 500–1000 cycles and have largely replaced NiCd batteries. Self-discharge was historically high but modern low-self-discharge (LSD) NiMH cells (Eneloop type) retain 70–85% capacity after a year. NiMH cells are safe, non-toxic, and suitable for handheld radio battery packs.

Lithium-Ion and Lithium Polymer (Li-ion / LiPo, Rechargeable)

Li-ion and LiPo cells have a nominal voltage of 3.6–3.7 V with excellent energy density — more energy per kilogram than any other common rechargeable chemistry. They are used in modern handheld transceivers, portable power banks, and field operation kits. LiPo cells can be formed into flat flexible packs. Both require a dedicated charger that controls current and voltage precisely; overcharging, overdischarging, or short-circuiting can cause thermal runaway and fire.

Lithium Iron Phosphate (LiFePO4, Rechargeable)

LiFePO4 cells have a nominal voltage of 3.2 V (12.8 V for a 4-cell pack — a drop-in replacement for 12 V lead-acid). They offer 2000–5000 cycle life, excellent thermal stability, and a very flat discharge curve that holds voltage until nearly depleted. LiFePO4 is increasingly popular for portable and emergency ham radio power due to its weight advantage over SLA (about one-quarter the weight) and long service life.

Sealed Lead-Acid (SLA / AGM, Rechargeable)

SLA batteries have a nominal voltage of 2 V per cell (12 V for a 6-cell pack) and are available in capacities from 1.2 Ah to hundreds of Ah. They are heavy but inexpensive, tolerant of overcharging (within limits), and widely available. AGM (Absorbent Glass Mat) construction makes them spill-proof and suitable for any orientation. SLA batteries self-discharge about 3% per month and should not be left in a discharged state — sulfation permanently reduces capacity. They are common in shack power backups and emergency kits.

Capacity and Voltage

Battery capacity is measured in ampere-hours (Ah) or milliampere-hours (mAh). A battery rated at 10 Ah can theoretically supply 10 A for 1 hour, or 1 A for 10 hours, or 0.5 A for 20 hours. In practice, higher discharge rates reduce effective capacity — a battery rated 10 Ah at the 20-hour rate may only deliver 7–8 Ah when discharged in 1 hour.

The terminal voltage of a battery drops as it discharges. The nominal voltage is the typical mid-discharge voltage. Equipment has a minimum operating voltage below which it shuts down or malfunctions; the battery is considered depleted when its voltage reaches this threshold, even if some chemical energy remains.

Discharge Curves

A discharge curve plots battery voltage against time (or percentage of capacity discharged) at a constant current. The shape of the curve tells you a great deal about how a battery will behave in use.

A flat discharge curve (LiFePO4, NiMH plateau) means the equipment receives nearly constant voltage throughout the discharge cycle, making it easy to predict remaining runtime. A sloping curve (alkaline, SLA) means voltage decreases steadily — equipment may perform differently at the beginning of a discharge cycle than at the end.

The knee of the curve is where voltage drops sharply toward the end of discharge. Below this point, capacity depletes rapidly and the battery should be recharged or replaced promptly.

Battery Life Calculator

The basic battery life formula is:

Operating Time (hours) = Battery Capacity (Ah) ÷ Average Current Draw (A)

This gives a theoretical maximum. In practice, account for efficiency losses, temperature effects, and the fact that some capacity is unavailable near the cut-off voltage. A realistic estimate multiplies the result by 0.8–0.9.

Series and Parallel Connections

Batteries in Series

Connect the positive terminal of one battery to the negative terminal of the next. Total voltage = sum of individual voltages. Capacity remains the same as a single battery. Example: four 3.2 V LiFePO4 cells in series give 12.8 V with the capacity of one cell.

Batteries in Parallel

Connect all positive terminals together and all negative terminals together. Voltage remains the same as a single battery. Total capacity = sum of individual capacities. Example: two 20 Ah, 12 V SLA batteries in parallel give 12 V at 40 Ah.

Charging and Safety

Each battery chemistry requires a specific charging method and voltage. Using the wrong charger can damage the battery or create a safety hazard.

• SLA/AGM: Constant voltage charging at 13.8 V (float) or 14.4–14.7 V (absorption). A smart charger with a float maintenance stage prevents sulfation and overcharging.
• NiMH: Constant current with negative delta-V termination or temperature cutoff. Trickle charging at C/10 is safe long-term. Do not use NiCd chargers on NiMH cells.
• Li-ion/LiPo: Constant current / constant voltage (CC/CV) charging to exactly 4.2 V per cell. Never exceed 4.2 V; never discharge below 2.5 V. Use only a charger designed for Li-ion. Never charge a damaged, swollen, or punctured LiPo cell.
• LiFePO4: CC/CV charging to 3.6–3.65 V per cell (14.4–14.6 V for a 4S pack). Requires a LiFePO4-specific charger — a standard lead-acid charger may overcharge these cells.

Ham Radio Applications

Portable and SOTA Operation

Summits on the Air (SOTA) and portable operators need the best energy-to-weight ratio. LiFePO4 packs and Li-ion power banks have largely replaced SLA batteries for field use because they weigh a fraction of the equivalent SLA capacity while maintaining similar or better performance.

Emergency Communication (EmComm)

ARES and RACES operators must be prepared to operate without commercial power. A 100 Ah SLA or LiFePO4 battery bank combined with a solar panel provides days of HF operation. The battery life calculator is an essential planning tool — knowing how long your battery will last at your expected current draw lets you size the system correctly.

Mobile Installation

Mobile transceivers draw from the vehicle battery and alternator. High-power transceivers should be wired directly to the battery with appropriate fusing, not through the fuse box, to avoid voltage drop and interference from other vehicle systems.