Factors Affecting A Decrease in Battery Life

It is difficult to compare accurately burn times/lighting durations between different manufactures hands-free lighting products since each manufacturer’s reference figures that show their product offering to have an advantage over competitive products. Some manufacturers state statistics of burn time calculated to times long after the emitted light output is useful (down to the last photon). Petzl clearly states it operates a policy whereby it ceases to consider a light effective when the lighting level (for standard hands-free lighting) decreases below 0.25 lux at a distance of 2 metres. This figure is selected as an approximate equivalence to the lux value generated on a dark night by a full moon. They consider this light output the minimum level that a hands-free lighting device should deliver in order to be fit for purpose.

Petzl operate an extensive testing procedure to produce their advertised statistics. Tests are conducted in a laboratory on five identical headtorches selected randomly straight from the production line. These headtorches are individually tested with two new sets of batteries, identical to those supplied with the product. Since temperature fluctuations can affect results (particularly the rate of discharge from battery technologies), the test environment is controlled at 20° Celsius to ensure statistically significant results. These ten sets of statistically reliable results are averaged across each parameter to provide the final definitive advertised light performance statistics. This rigorous and clearly defined testing process provides precise performance indicators, which can be effectively evaluated across various products within the range by the consumer to match their requirements against perform...

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...primary battery (especially alkaline) as they generally suffer less self-discharge when not in use than secondary batteries.

If the device operates using secondary batteries then there are significantly more potential causes of duration differentiation than standard primary batteries. In addition to the aforementioned issues that affect all batteries there are more issues that are secondary batteries specific. Issues that affect secondary batteries are:

• Cell age

• Battery cycle life

• Initial charge level

• Cell condition / past treatment

• Memory effect (especially NiCd)

• Loss of electrolyte

• Venting (a release of battery active chemicals)

These can be seen as the major reasons behind a decrease in battery life, thus burn time/light duration. Some of these issues do affect primary batteries, e.g. venting, however generally they are rechargeable only.