The effect of zapping

Remote control (RC) racing enthusiasts have experimented with all imaginable methods to maximize battery performance. One technique that seems to work is zapping the cells with a very high pulse current. Zapping is said to increase the cell voltage by 20 to 40mV under a 30A load. According to experts, the voltage gain is stable; only a small drop is observed with usage and age.

During the race, the motor draws 30A from a 7.2V battery. This calculates to over 200W or close to a quarter HP of power. The race lasts about four minutes.

According to experts, zapping works best with NiCd cells. NiMH cells have been tried but the results are inconclusive. Zapping is done with a 47,000mF capacitor charged to 90V. Best results are achieved if the battery is cycled twice after treatment, then zapped again. Once in service, zapping no longer improves the cell's performance. Neither does zapping regenerate a cell that has become weak.

Companies specializing in zapping batteries use top quality Japanese-made NiCd cells. The cells are normally sub-C and are handpicked at the factory. Specially labeled, the cells arrive in discharged state with open cell voltages of 1.11 to 1.12V. If below 1.06V, the cell is suspect and zapping does not work well.

There are no apparent side effects to zapping but the battery manufacturers remain non-committal. No scientific explanation is available and only little is known on the longevity of the cells after treatment.

How to prolong lithium-based batteries

Battery research is focusing heavily on lithium chemistries, so much so that one could presume that all future batteries will be lithium systems. In many ways, the Lithium-ion (Li-ion) is superior to nickel and lead-based chemistries.

A Li-ion battery provides 300 to 500 discharge/charge cycles or two to three years of service from the time of manufacturing. The loss of battery capacity occurs gradually and often without the knowledge of the user. There are no remedies to restore Li-ion batteries when worn out.

Li-ion prefers a partial rather than a full discharge. Avoid depleting the battery fully too frequently. Instead, charge more often or use a larger battery. There is no memory to worry about.

Although lithium-ion is memory-free in terms of performance deterioration, engineers often refer to "digital memory" on batteries with fuel gauges. Repeat small discharges with subsequent charges do not allow the calibration needed to track the chemical battery with the fuel gauge. A deliberate full discharge with recharge every 30 charges, or so, will correct this problem. Letting the battery run down in the equipment to the cut-off point will do this. If not done, the fuel gauge becomes increasingly less accurate.

The aspect of aging is an issue that is often ignored. A time clock starts ticking as soon as the battery leaves the factory. The electrolyte slowly 'eats up' the positive plate, causing the internal resistance to increase. Eventually, the cell resistance reaches a point where the battery can no longer deliver energy, although the battery may still contain charge.

The speed by which Li-ion ages is governed by temperature and state-of-charge. The most harmful combination is full charge and high temperature. If possible, store the battery in a cool place at a 40% charge level. Figure 1 illustrates the capacity loss as a function temperature and charge level.


Figure 1: Permanent capacity loss of Li-ion as a function of temperature and charge level.
High charge levels and elevated temperatures hasten the capacity loss. Improvements in chemistry have increased the storage performance of some Li-ion batteries.

Simple Guidelines

- Avoid full frequent discharges; recharge Li-ion more often. There is no memory to worry about.
- Although memory-free, apply a deliberate full discharge once every 30 days on batteries with fuel gauge to calibrate the battery. If not done, the fuel gauge will become increasingly less accurate.
- Keep the Li-ion battery cool. Never freeze the battery. Avoid a hot car.
- For prolonged storage, keep the battery at 40% charge level.
- Avoid purchasing spare Li-ion batteries for later use. Observe manufacturing date. Do not buy old stock, even if sold at clearance prices.