Figure 3 summarizes the cost to generate 1kW of energy from AA alkaline cells, a sealed Nickel-cadmium battery, a combustion engine, a fuel cell and the electrical grid. We take into account the initial investment, add the fuel cost where applicable and include the eventual replacement of each system.

Figure 3: Cost of generating 1kW of energy. This takes into account the initial investment, fuel consumption where applicable, maintenance and eventual replacement of the equipment. The cheapest power source is the utility; the most expensive is primary batteries.

The fuel cell offers the most effective means of generating electricity but is expensive in terms of cost per kWh. This cost becomes economical when compared with portable batteries, however. For vehicular and stationary applications, the fuel cell is considerably more expensive than the combustion engine. The costing information is based on current estimates and assumptions.

Primary versus secondary batteries

Consumer market put aside, the largest users of primary batteries are defense organizations and emergency services. High energy density, long storage and simple usage put aside, one of the most important attributes of the primary battery is combat readiness. No charging and priming is required before use. Logistics are simple and portable energy can be made available at remote distribution points that are unmanned and have no electricity. Disposal is easy because little toxic material is used.

Because of one-time use, the cost of the primary battery is about 30 times higher than that of rechargeables. The pricing becomes even more exorbitant if the packs are replaced after each mission, regardless of length. A General of the US Army said that half of the batteries discarded still have 50 percent energy left. Discarding partially used batteries is widespread because keeping track of these packs is time-consuming and awkward. It is much simpler to issue fresh packs before each activity.

Reading the state-of-charge (SoC) of primary batteries is possible. The most basic method is measuring the terminal voltage but the result is inaccurate. A better method is counting the out-flowing energy units, also known as coulombs. This requires a circuit and display on the battery. Due to high cost and inherent inaccuracies, especially during pulsed loading, this method is seldom used on primary batteries.

A more accurate SoC measurement is possible with quick-test instrument in which the chemical integrity of the battery is examined. Each battery type requires a reference matrix, which can be stored in the designated adapters that are used for the battery interface. The test lasts a few seconds and is non-invasive.

During the last ten years, armies and emergency response teams have gradually been switching to rechargeable batteries. The reasons are improvements in battery technology, better charge methods and more readily available charge power. But the most important single reason is cost.

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.