This is Paper B of the C02 note on tactical and military radios, taking the working profile from Paper A and turning it into a pack design: how many cells, what capacity, and what margin the radio needs to run its mission. It follows the sequence an engineer actually uses - define the mission and duty convention, convert the three operating states into an average current, choose the cell configuration for the required voltage, apply cold and end-of-life deratings, check the pulse and thermal limits, and then define the field charging arrangement. Two worked examples are shown end to end: a handheld radio under the 5-5-90 convention and a patrol radio under the 1:9 convention. Every number in them is explicitly labelled illustrative and built from currents in the range of published datasheets, not a specification for a named product; the binding values for a real project are the radio's own datasheet and the agreed pack drawing.
Key fact 1. Sizing starts from the mission, not the mAh label. The inputs are the radio's currents in standby, receive and transmit, the duty convention that weights them, the required runtime in hours and the operating temperature. Two conventions appear in the field: 5-5-90 (5 percent transmit, 5 percent receive, 90 percent standby) and 1:9 (one part transmit, nine parts receive, with no separate standby). Runtime figures are only comparable when the convention and temperature match.
Key fact 2. Average current is a weighted sum, and capacity is average current multiplied by hours. In the illustrative handheld example below, currents of 0.08 A standby, 0.3 A receive and 1.6 A transmit under 5-5-90 give an average of 0.167 A, so a ten-hour shift needs 1.67 Ah of charge. The transmit state is only 5 percent of the time but contributes close to half the average current, which is why a heavy talker's runtime diverges quickly from the published figure.
Key fact 3. The cell count is set by the voltage. Each sealed nickel cell is 1.2 V, so six cells give 7.2 V, eight give 9.6 V, ten give 12 V and twelve give 14.4 V. Professional handheld packs are commonly 7.2 V or 9.6 V, while larger field and manpack systems use higher configurations. The radio's accepted battery range, not the charger alone, determines which configuration is legal for the design.
Key fact 4. Nameplate capacity must exceed the mission number because usable capacity shrinks. Cold temperature reduces discharge performance and a pack loses capacity over its service life, so the design applies derating factors and keeps a margin. In the worked example the 1.67 Ah mission need is divided by illustrative cold and end-of-life factors of 0.85 each, giving a required nameplate of about 2.31 Ah before a standard cell is selected.
Key fact 5. The pack is a mechanical and safety assembly, not just cells. It must deliver the transmit pulse without the voltage collapsing, control its temperature under charge and discharge, and carry protection such as a PTC and resettable fuse inside the radio's defined geometry. Field charging is defined at the same time, including vehicle charging from the 28 V MIL-STD-1275 bus and battery eliminators that remove the battery from the load path entirely.
The first design decision is which duty convention represents the user. The 5-5-90 convention comes from land-mobile practice and is built around long standby periods with short calls, which suits a handheld carried through a shift. The 1:9 convention comes from HF and patrol practice, where the radio is continuously listening and periodically transmits, with no separate standby state. The temperature is recorded alongside the convention because a cold or hot measurement changes the result, and the required runtime is stated in hours from the mission rather than inferred from a competitor's headline. A pack sized against the wrong convention will be either unnecessarily large or short on the actual mission.
With the three state currents and the convention fixed, the average current is the weighted sum of the states, and the mission charge is that average multiplied by the hours. The illustrative handheld example uses currents of 0.08 A in standby, 0.3 A in receive and 1.6 A in transmit, all presented as illustrative values in the range of published portable radios rather than measurements of one product. Under 5-5-90 the average is 0.05 times 1.6 for transmit, plus 0.05 times 0.3 for receive, plus 0.90 times 0.08 for standby, which equals 0.167 A. For a ten-hour shift the required charge is 0.167 times 10, or 1.67 Ah.
The weighting explains why duty changes matter so much. The transmit segment occupies only 5 percent of the time but contributes 0.08 A of the 0.167 A average, close to half of it; a user who transmits 10 percent instead of 5 percent moves the average upward even though the shift length and the radio are unchanged. This is the mechanism behind the warning that a published runtime is a convention-dependent result, and it is why the actual talk pattern is collected before sizing rather than assumed from a datasheet.
Once the charge requirement is known, the series count is chosen from the voltage. The sealed nickel cell is 1.2 V nominal, so the arithmetic is direct: six cells in series give 7.2 V, eight give 9.6 V, ten give 12 V and twelve give 14.4 V. Parallel strings increase capacity where the geometry allows, but the voltage is always set by the series count. A handheld whose electronics accept a range around 6 to 9.6 V is typically designed around a six-cell 7.2 V pack, while a manpack or field system may need a higher configuration. The chosen count must sit inside the radio's accepted input range across the full discharge, including the lower voltage at end of charge, rather than only at nominal.
| Cells in series | Nominal voltage | Typical pack role |
|---|---|---|
| 6 | 7.2 V | Handheld professional radios |
| 8 | 9.6 V | High-voltage handheld packs |
| 10 | 12 V | Field and accessory systems |
| 12 | 14.4 V | Manpack and higher-tier packs |
The mission number is usable charge, but nameplate capacity is larger because two effects reduce what the pack can deliver. Cold temperature slows the electrochemical reaction and lowers the effective capacity, and over the service life the pack loses capacity through cycling and ageing. The design applies derating factors to cover both and keeps a margin for variation. In the illustrative example, factors of 0.85 for cold and 0.85 for end of life are applied, so the usable fraction is 0.85 times 0.85, or 0.7225; the required nameplate is the 1.67 Ah mission need divided by 0.7225, which is about 2.31 Ah. A standard cell at or above that figure, in the required geometry, is then selected.
Capacity is not enough on its own: the pack must deliver the transmit pulse with the voltage held above the radio's cutoff. The design checks the discharge curve at the transmit current, including the short high-current pulse at the worst state of charge, and confirms the pack temperature stays within limits under repeated pulses. Protection is built into the assembly: a PTC limits current under fault or overtemperature, a resettable fuse covers overcurrent, and the pack geometry and retention keep the cells and contacts secure under shock and vibration. The protection is sized to the radio's real pulse rather than to a generic peak, and the housing is the radio's defined shape so the pack cannot be replaced by loose cells.
Nickel packs need a defined charge regime because overcharge heats the cells; a charger terminates on the negative voltage change or temperature rise characteristic of nickel chemistry and controls the charge rate for field use. Vehicle charging works from the 28 V military bus under MIL-STD-1275, whose transients, spikes and surges are handled before the charger, and a battery eliminator lets the radio run directly from the vehicle supply so the battery is not cycling during mounted operation. Airborne platforms instead use MIL-STD-704. The charger and eliminator are part of the pack design package rather than afterthoughts, because a pack that cannot be recharged in the field does not deliver its calculated runtime.
The same sequence under the patrol convention shows how the inputs change the result. The illustrative patrol radio draws 4 A on transmit and 0.5 A on receive, presented as illustrative values in the range of higher-power manpack radios. Under 1:9 the average is 0.1 times 4 plus 0.9 times 0.5, or 0.85 A; an eight-hour patrol therefore needs 6.8 Ah. Applying the same 0.7225 derating gives a required nameplate of about 9.4 Ah, which is the same arithmetic as the handheld but at a much larger capacity because the convention has no standby state and the transmit current is higher. This mirrors the published example of a fielded patrol manpack whose vendor offers a 13 Ah NiMH pack rated around 50 hours under 1:9, while showing why a single standard capacity cannot be reused across conventions without rechecking the math.
| Design input | Why it is needed |
|---|---|
| Standby / receive / transmit currents | Build the three-state average current |
| Duty convention and talk pattern | Weight the states; choose 5-5-90 or 1:9 |
| Runtime in hours and temperature | Set the mission charge and cold derating |
| Accepted voltage range and geometry | Fix the series count and housing |
| Pulse current and charging arrangement | Check voltage collapse and field recharge |
The sizing method applies wherever a sealed nickel pack is a genuine fit, and the scope is stated honestly rather than stretched. Frontline US handhelds are designed around lithium packs, so Weijiang does not present these calculations as a lithium replacement for deployed combat radios. The realistic applications are training and garrison radios, patrol HF where the vendor offers NiMH, professional and security packs, accessories and logistics-sensitive buyers who value the not-restricted shipping under UN 3496 and IATA A199. Within that scope the same cell-count, capacity and derating sequence produces a defensible pack, with the exact values always tied to the radio's datasheet rather than carried over from another project.
Because mAh is nameplate capacity, not the mission result. The runtime depends on the duty convention, the temperature and the deratings, and two packs with the same mAh can differ in voltage, geometry and pulse capability. The design rebuilds the average current and the required nameplate from the radio's actual inputs rather than matching a label.
More than its share of time suggests. In the illustrative 5-5-90 example the 5 percent transmit segment contributes close to half of the average current because its current is far above standby and receive. Doubling the talk time therefore raises the average noticeably and shortens the runtime even with the same pack.
Because only a fraction of the nameplate is usable. If cold and end-of-life factors leave 0.7225 of the capacity available, the nameplate must be the mission need divided by 0.7225, not multiplied; multiplying would size a pack that is too small. The factors themselves are cell and vendor dependent and are agreed rather than assumed.
A battery eliminator can, by running the radio directly from the 28 V vehicle bus and removing the battery from the load path; a vehicle charger instead recharges the installed battery. The first must handle the MIL-STD-1275 transients and the second must follow the nickel charge termination, so the two are specified separately.
The radio's retention, contacts and sealing are designed around one pack shape, and the environmental ratings assume the correct housing. A generic cell or an oversized pack cannot meet the retention and ingress requirements, which is why the pack is built to the defined geometry even when the electrical capacity could be achieved another way.
The duty conventions and the 5-5-90 profile are documented in manufacturer and industry material, and the 1:9 convention appears in patrol and HF vendor datasheets. The currents used in the worked examples are illustrative values in the range of published radio datasheets, and every worked number is shown as a calculation rather than a measurement of a named product; the patrol example is cross-checked against the published fielded manpack offering a 13 Ah NiMH pack under 1:9. Voltage configurations follow the 1.2 V sealed nickel cell, and charge termination practice follows nickel-cell technical references. Vehicle and airborne power reference MIL-STD-1275 and MIL-STD-704, and the nickel cells and packs are qualified to IEC 61951-2 and IEC 62133-1 and ship under UN 3496 with the IATA A199 not-restricted air path. No statistics have been invented.
Weijiang Power supplies sealed NiMH cells and assembled NiMH packs for training, garrison and patrol tactical radios and professional security packs, sized from the radio's currents, duty convention, runtime and temperature and built to its geometry with PTC and resettable-fuse protection. The cells are qualified to IEC 61951-2 and IEC 62133-1 and the packs ship under UN 3496. Send us your radio model, accepted voltage range, state currents, duty convention, runtime, temperature and charging arrangement, and we will work through the average current, cell count, derated nameplate and pulse design and support the evidence for your evaluation. See the Weijiang NiMH product range for standard pack formats, or contact our OEM team with the radio specification and load profile.
