As the Army extends its battlefield communications network down to the individual soldier, it has greatly improved troops’ ability to access and share information. This has created an entirely new challenge — the need for sustainable portable power.
The ongoing need to improve battery efficiency and reduce weight still holds, but the Army also is interested in fielding novel technologies that accomplish more than simply removing pounds from a soldier’s load, said Steve Mapes, product lead for soldier power at Program Executive Office Soldier.
“As you have effectively closed that capability gap for combat information, a consequence is you have created an entirely new one for power and energy,” Mapes said during a recent interview at Ft. Belvoir, Va. “As the Army moves toward bringing entire brigades into the network, we have to keep pace with that new Army strategy by providing the necessary support equipment to sustain those formations.”
Mapes likened a networked radio to leaving a cell phone on during a plane ride at 30,000 feet. The constant search for a signal will drain the phone’s battery much more quickly and it will almost certainly be dead or significantly depleted by the time the plane lands, he said.
“You’re burning through batteries on a networked radio at a rate of two to four hours,” he said. “A battery that is designed to last eight to 10 hours out of the network is consumed in two to four hours on the network.”
The 2.5-pound, 150 watt-hour conformal battery was born out of the necessity to keep radios networked without weighing soldiers down with perhaps a dozen disposable batteries per day.
“There was no ‘prior-to-this’ battery. … There was no need for such a capability with the urgency we have today because you didn’t have all your guys running around with networked radios,” Mapes said. “We’re not necessarily replacing something. We are responding to an entirely new Army strategy with completely new architecture and support equipment.”
The conformal battery is changed once every 24 hours as opposed to swapping out multiple batteries every six to eight hours, which cuts downtime and reduces the risk that a soldier will lose power to peripheral devices, said Steve Aviles, senior operations research analyst for the Operational Energy Branch of the Soldier Division at the Maneuver Center of Excellence in Ft. Benning, Ga.
“Even if we could charge our radio batteries and we didn’t have to bring extras out, we would still be changing those out every six to eight hours,” he said.
Introducing considerably more radios to the network also made primary, disposable batteries prohibitively expensive for the Army, he said. Without a state-of-charge indicator, soldiers did not know how much energy was left in their primary batteries. Each time they ventured outside the wire on patrol, they would throw away their old batteries and pop in brand new ones out of the package, he said.
The conformal batteries are part of capability set 13 — the Army’s first attempt to bring entire brigades into the network. It introduces networked battlefield communications gear to units at the team-leader level and above.
“Power is a growing issue and it always has been … but it has spiked over the last three or four years and it has significantly spiked in capability set 13, when we actually did what we’ve been planning for a decade — we actually put soldiers in the network,” Mapes said.
So far, four combat brigades have been equipped with the technology suite that includes radios, power management systems, attendant battery chargers and other support equipment. Full funding and fielding is scheduled for fiscal year 2016 for procurement and total small unit power should be completed in 2017, Mapes said.
The conformal battery is a flexible, multi-cell rechargeable power pack that fits into a soldier’s chest or side body armor pouch over the protective plate. It has been proven to withstand more than 300 bends in excess of two inches without the interior cells or outside casing being broken. It also improves on the 5590 soldier-radio battery by providing a series of lights that show how much power the battery holds. The power packs do not offer ballistic protection, but if shot will continue to provide power because each internal cell is independent of the others.
Soldier feedback is informing improvements that Army engineers and industry are using to design the next iteration of the battery and support equipment. They are also providing information on how best to use the equipment in the field, Mapes said.
“The guys never cease to amaze and inform us of the tactical application of how this is used on the battlefield,” he said. “Soldiers don’t only consider it as power worn, they consider it to be power portable. So we go into a forward operating base and a guy has his laptop out, and it’s connected not to a power strip that’s pulling from a generator, but to a conformal battery.”
Rechargeable batteries require battery chargers. Soldiers need ones that operate in sparse environments where a wall outlet or even a car battery may not be available. The squad power manager — another element of capability set 13 — answers that need.
The SPM is basically a collection of power cords that can recharge a conformal battery using anything from a vehicle’s cigarette lighter to a solar blanket. A commander with the 82 Airborne Division in Afghanistan was able to completely eliminate battery resupply to his combat outpost using nothing but the SPM and solar blankets, Mapes said.
“They were at static mortar sites, but the note here is that in the commander’s logistics plan, he no longer had to account for moving batteries to those sites,” Mapes said. “They were able to achieve what we have been trying to achieve for years and what we are still trying to achieve — autonomous operations.”
The modular universal battery charger offers another option for recharging conformal and traditional radio batteries. It is another technology that resulted directly from the Army’s effort to bring individual soldiers into the network, Mapes said.
“At this scale, it replaces nothing because there were never so many radios in the formation. There was never a requirement for so many chargers,” he said. “So we had to come up with a way to support all these rechargeable batteries.”
Designed for use in more static positions, the device has charging bays for both radio and conformal batteries and is issued with a 120-watt solar blanket. Based on soldier feedback, the MUBC’s size has been cut in half and its power throughput doubled from 150 watts to 300 watts.
It and the SPM also now have harvesting capability. A soldier can take a half-dead primary 5590 battery and transfer the remaining energy to a rechargeable battery.
The conformal batteries are made by Palladium Energy, which produces the lithium-ion prismatic cells. As in the commercial market, battery weight, size and power are limited by the periodic table.
“When lithium ion came on the scene, it was a significant leap,” Mapes said, noting that the chemistry allowed for greater energy storage than alkaline batteries and the ability to recharge. “The chemistry of the battery is going to drive possibilities for the future. We are looking to emerging chemistry and innovation because current technology can only take us so far.”
Industry is already experimenting with battery chemistries that improve energy density and stability along with extending shelf life and length of charge. Energizer, the commercial battery giant, has done just that with its lithium-iron disulfide batteries, called the L91.
The double-A is already the military’s preferred cell for use in small electronics because of its advantages over traditional alkaline batteries, said Bob Devine, the company’s L91 technology manager. The military purchases about 2 million double-A cells per year, he said.
Energizer has been working with the Defense Department for nearly a decade to develop lighter, more stable battery chemistries like lithium-iron disulfide that are 37 percent lighter than the alkaline cells they replace, among other advantages.
“We have been trying to improve capacity and reliability,” Devine said. “From a capacity standpoint, our focus has been on making adjustments to the overall construction of the battery and removing inert material and replacing it with active constituents.”
The L91, which is commercially available, is commonly used in gear like the defense advanced GPS receiver, AN/PAS-13C thermal weapon sight, night vision goggles and monoculars and LED flashlights.
A major advantage the lithium-iron disulfide chemistry has over other cathode-anode combinations is the range of temperatures at which it can provide power. The L91 battery has been tested from negative 40 to 60 degrees Celsius, said Matthew Wendling, a staff technology engineer at Energizer.
“This chemistry is generally extremely stable, which not only contributes to shelf performance but the safety of the battery,” Wendling said. “This is not a lithium-ion product. The chemistry is much more stable.”
Alkaline batteries have a tendency to leak and bleed energy in hot temperatures, he said. They simply seize up at temperatures below freezing. Lithium-iron disulfide will do neither, he said. It also has a shelf life of upwards of 40 years without losing more than 20 percent of charge, which would allow the Army to stockpile them without worry, he said.
“We have actual, real-time shelf data of 20-year-old batteries that still perform almost as if they are new,” he said. “They are essentially leak proof, which in this case is important so as not to damage some potentially very expensive military equipment.”
Energizer has been making L91 batteries for two decades, in which time the cell has been enhanced from 200 watt-hours per kilogram to 300 watt-hours per kilogram. The company is limited by how much lithium it can put into a single battery, but has shown up to 326 watt-hours in compositions made specifically for the military, said Mike Mansuetto, who also manages the L91 technology.
“For years, the commercial market has been a horsepower race of how much power can be put into the finite package of a double-A cell,” he said. “Some of it is brute force in terms of putting more materials into the battery. We also optimized the cell by reducing the weight of the container materials and other things. The double-A form factor is a fixed volume — double-A cavities are double-A cavities — so there’s only so much material we can force into them.”
Soldiers have determined that about 150 watt-hours is the ideal amount of power to carry at a time, Mapes said. The Army, therefore, is undertaking a similar engineering challenge in squeezing that much energy storage into a smaller battery.
PEO Soldier and Research, Development and Engineering Command are seeking “to further improve the design by reducing even more the weight and volume of the battery,” Mapes said. “We’re working hard with RDECOM and industry to get it down from 2.5 pounds to below 2 pounds. As technology improves, we believe within the next five years we can reach that goal.”Photo Credit: Thinkstock