Best Practices in Lithium Battery Management

Lithium batteries have some great properties, and some *not so great* properties.

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For ultra small devices―like the AltimeterOne―that include sensors, displays, and other sophisticated components yet need to be as small and light as possible, there really isn’t a better alternative to Lithium chemistry batteries. While there are some rather small Alkaline, NiCd, and NiMH batteries available (some as coin cells), they are typically limited in voltage (1.2-1.5V), current (a couple of milliamps), and capacity (<10mAh). And so we need to overcome the challenges of Lithium cells.

The best way to do this is to design for Lithium from the onset, and compensate wherever possible for the drawbacks. For instance, the AltimeterOne has three independent circuits to ensure safe operation. One is mounted directly to the power cell to strictly limit both charge and discharge current, and to shut the cell down if its temperature rises too far. The second circuit oversees the charging of the cell, and limits the maximum current that can be applied―starting very slowly at first, and stopping the charging process entirely once it detects that the charging is complete. The final circuit monitors the voltage of the battery and lets the microprocessor know that it’s time to remind the user to recharge.

As for cost, the batteries and their support components have been dropping in price as the technology has matured, and as more alternative suppliers have come on line. There is now plenty of competition among battery and support chip vendors—and that has brought prices down nicely.

Notice that the cost to provide recharging capability for the Altimeter One is reduced by the clever incorporation of a charging plug into the device itself, eliminating the cost and complexity of an extra cable or adapter!

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