DIY

WORKSHOP

ON BATTERIES

How to decide which batteries will run your project best. By Limor Fried

If knowledge is power, then knowledge of batteries is power squared! Here’s what I know about disposable and rechargeable batteries and their tradeoffs.

Measuring Batteries There are a few ways you can measure batteries of different types. Here’s what I’ll be comparing:

Photography by Sam Murphy

Size There are standard sizes such as AA and 9V, an assortment of coin cells, and special rechargeable power modules for specific products.

Voltage Labeled voltage and actual voltage differ. An alkaline labeled “ 1.5V” actually starts out at 1.6V, quickly drops down to 1. 5, and then drifts down tery’s voltage derives from its chemistry. Alkalines are always 1.5V, lead-acid cells are 2V, and lithium

cells are 3V. Batteries with higher voltages like 12V contain multiple connected cells in one package.

Reusability Rechargeable batteries vary in the number of recharge cycles possible during their useful life, usually in the hundreds. But you need to use a high-quality charger, one with sensors; cheap chargers can kill your cells. NiCd and NiMH rechargeables have lower voltages than alkalines,so test them before using them as replacements.

Power capacity determines how much power a battery holds. On the packaging, this is listed in milliampere-hours (mAh), a measure of charge capacity. To convert this to power capacity (watt-hours or Wh), multiply by the voltage.

Make: 151