Survival radios are the lifelines for warfighters placed in critical situations. By increasing the energy capacity and allowing for replacement and recharging of the battery cells, these lifelines can literally be extended. By giving the warfighter extended energy capability, this gives them a higher chance of survival and recovery. The sustainment redesign of the battery packs (Figure 5-1) for the AN/PRC-112D survival radios required clear definition of and adherence to interface requirements and specifications. In addition, significant cost and logistics benefits were achieved by incorporating several commercial off-the-shelf (COTS) components into the redesign.

COTS design elements included the use of AA battery cells within a reusable battery case (Figure 5-2), while ensuring that new battery pack performance met or exceeded the functional criteria of the original battery. Additionally, a major “pass-through” (no redesign required) benefit was gained due to the ongoing improvements incorporated by the COTS suppliers (i.e., the AA battery cell manufacturers) as they continuously enhance their products in the competitive commercial business environment.

For example, recently developed rechargeable nickel-metal hydride battery cells now have twice the energy density (1600 mAh vs. 700 mAh) contained within the same AA cell dimensions of the older NiCd batteries. Also, the newer non-rechargeable lithium photo/electronic AA battery cells at 2900 mAh are greater than 40 percent higher in capacity than alkaline battery cells. Each of these benefits will now be reaped automatically by the redesigned radio.

Additional COTS battery cell characteristics presently being improved include:

• Number of possible recharge cycles per cell is approaching 1000
• Decreased charging times
• Expanded temperature performance range from -40°C to 95°C
• Extension to a 10-year storage life
• Higher discharge rates for heavier load conditions

As long as the redesigned AN/PRC-112 battery case adheres to the functional requirement of loading eight AA batteries, per the industry standard cell dimension specification, it can readily reap any and all of these ongoing enhancements.

Per DoD specifications, another COTS connector component was chosen to interface the battery pack to an optional external charger. This component had to meet the following additional requirements:

• Two-pin female connector
• Waterproof to a depth of 50 feet
• Recessed installation beneath the surface of the main battery pack housing Based on these requirements, a LEMO model HGG series 00 connector was selected. This connector provided additional features of being both self-keying and self-locking upon insertion.

After qualification testing to ensure compliance with the environmental conditions (Table 5-1), several other COTS parts were approved for the battery terminal O-ring and the gasket sealing material (between the lid and housing when replacing battery cells). Also, the AA cell battery contact springs and pressure vent were selected from standard commercial parts.

One feature of the battery pack that could not be handled by a COTS component was the unique mechanical and electrical interface between the battery pack and the AN/PRC-112 radio (Figure 5-3). It is specified to be in accordance with MIL-PRF-4947/10A(CR), which requires a custom-molded part with tightly-dimensioned alignment /locking tabs centered around two gold-plated, beveled terminal pins.

The production tooling for the new custom battery case housing and three other custom subparts was contracted for only after the design was confirmed by a thorough evaluation of the 3D design model documentation and several mechanical mock-ups. This phase represented both the longest lead-time and the most expensive portion of the R&D effort, which emphasized the premium paid for the use of custom-designed components vs. COTS.

Summary
The original technical requirement of 12 hours mission time (assuming a 90% receive, 10% transmit mode of operation) for the legacy AN/PRC-112 survival radio / battery pack combination has now been increased to a minimum of 20 hours for the upgraded version of the radio / battery pack. This increase in performance significantly improves the uptime of communication equipment which the warfighter relies upon.