In the US Army, rechargeable batteries have been used predominately for training. Officials are now exploring the suitability for combat missions. Rechargeables have advantages that go beyond cost issues. For one, the batteries can be re-used and do not burden the supply channels. In the absence of electric power, charging can be done through solar power, windmills and hand-crank generators. Even kinetic power is being explored in which an electric generator is built in the sole of the soldier's boot. Rechargeable batteries can keep communications going in areas where no supply of fresh batteries is possible.

Rechargeable batteries are not new to the armies - the Dutch Army has been using them for decades. Whereas the Dutch Army uses smaller packs for hand-held devices, the US Army uses larger batteries for backpack equipment. Beside chemistry and size, there are other differences in how the two armies manage the batteries in the field.

The US Army issues batteries with no maintenance program in place. If the battery fails, another pack is released, no questions asked. This has resulted in a high failure rate. The Dutch Army, on the other hand, has moved away from the open fleet system by making the soldiers responsible for their batteries. The change was made in an attempt to reduce waste and improve reliability. The batteries become part of the soldier's personal belongings.

Since adapting this new regime, the failure rate has dropped considerably and battery performance has increased. Unexpected down time has almost been eliminated. It should be noted that the Dutch Army uses exclusively NiCd batteries. Each pack receives periodic maintenance on a Cadex battery analyzer to prolong service life. Batteries that do not meet the 80 percent target capacity setting are reconditioned; those that do not recover are replaced. The US Army, on the other hand, uses NiMH batteries, which offer higher energy densities than NiCd but have a shorter service life.

Battery maintenance

With the switch to secondary batteries, some level of battery maintenance is require, a service that is best performed with a battery analyzer. Here are some field results on the use of battery analyzers:
At the conclusion of the Balkan War, the Dutch Army serviced all batteries at the Dutch Military Headquarters using Cadex 7000 Series battery analyzers. The army was aware that the packs were used under the worst possible conditions. Rather than a good daily workout, the NiCds were employed for short patrol duties lasting 2 to 3 hours per day. The rest of the time the batteries remained in the chargers for operational readiness. The batteries were 2 to 3 years old.

The capacity on some packs had dropped from 100 percent nominal to 30 percent. With the analyzer's recondition function, 9 out of 10 batteries were restored to full service. The Dutch Army sets the target capacity threshold for field acceptability to 80 percent.

The importance of exercising and reconditioning NiCd batteries with a battery analyzer is emphasized by another study carried out for the US Navy by GTE Government Systems in Virginia, USA. To determine the percentage of batteries needing replacement within the first year of use, one group of batteries received charge only (no maintenance), another group was periodically exercised and a third group received recondition. The batteries studied were used for two-way radios on the aircraft carriers USS Eisenhower, USS George Washington, and the destroyer USS Ponce.

With charge only (charge-and-use), the annual percentage of battery failure on the USS Eisenhower was 45 percent (see Figure 4). When applying exercise, the failure rate was reduced to 15 percent. By far the best results were achieved with recondition. The failure rate dropped to 5 percent. Identical results were attained from the USS George Washington and the USS Ponce. Recondition is a secondary discharge that removes the remaining battery energy by slowly draining the cells towards zero volts.

Figure 4: Replacement rates of NiCd batteries. The need to replace batteries decreases by three and nine-fold respectively when exercise and recondition is applied. These statistics were drawn from batteries used by the US Navy on the USS Eisenhower, USS George Washington and USS Ponce.