Lithium Polymer Battery Care and Maintenance

Lithium-Polymer (LiPoly) batteries, the type used in the NSRT_mk3 and VSEW_mk2 series of instruments, are used in almost every mobile application nowadays. They are small, light, and carry large amounts of energy, which makes them the battery of choice from cell phones to laptops, and ear buds to smart watches. However, Lithium-Polymer batteries have a few vulnerabilities that need to be minded to insure a long and fruitful battery life. This is especially the case when used in instruments that may be operated outdoors, over a wide temperature range, and over long periods of time.

Temperature

Operation and storage of a LiPoly battery at higher temperatures makes it age faster. This is especially true if the battery is operated above its absolute maximum rating of 60°C (140 °F). In that case the battery may be damaged in a short time.

Operation and storage of the battery below its minimum temperature rating of -20°C (-4 °F) will damage the battery very quickly.

State of Charge

Reaching a state of over-discharge can irreparably damage a LiPoly battery. There are multiple safeties to avoid that state in the NSRT_mk3 and VSEW_mk2 series of instruments. These safeties will power-down the instrument, first by firmware, and then by a hardware limiter in the battery itself, when the battery level goes below a safe level. However, any battery displays some amount of self-discharge, and when the battery’s low-level safeties engage it is only a question of time until the battery reaches a level of over-discharge that can damage it. There is a variable amount of margin, but the battery should not be left in that state for more than 1 to 2 weeks, especially if the temperature is low.

Battery damage

Battery damage usually means that the battery cannot keep its charge anymore. Many instruments will continue to work while connected to USB, but as soon as they are disconnected, they will stop working and reset themselves, thereby losing the time and being unable to record standalone.

In some cases, the battery may leak. This is especially damaging to the NSRT_mk3 series because the leakage of electrolyte will corrode the circuits of the instrument, damaging it irreparably. The VSEW_mk2 has a potted design, and that protects the circuits to a large extent.

How to avoid battery damage

To avoid battery damage, it is important to keep a close eye on its state of charge and temperature. To that end the user should check the following indicators:

• Battery temperature is displayed in the Settings panel of the Instrument Manager. The minimum and maximum temperature that the instrument has experienced are also displayed in that app.
• On instruments that are connected to the cloud, the battery temperature is reported every time the instrument connects to the cloud, and the temperature graph can be viewed. In that case it is easy to check if the instrument is experiencing temperature extremes over a day, a week, a month… etc.
• When a battery level becomes too low, the operation LED will start quickly blinking 4 times per second. When that occurs, the instrument should be recharged immediately.
• On WiFi-connected instruments and instruments that are connected to the cloud, an email alert can be sent when the battery level becomes too low. We strongly recommend the use of that email alert. When the alert is received the battery should be recharged immediately.
• Low-battery damage is of special concern with instruments that are WiFi-connected or connected to the cloud. WiFi communication create a large drain on the battery. So in cases where the instruments cannot keep a proper state of charge, for instance if their charger has been switched off, or the solar panel does not see the sun for long enough each day, the battery can drain very quickly to the switch-off level. At that point it may not take a long time to reach a state of over-discharge, especially if the temperature is low.
• Instruments that are left in storage, should be initially fully charged and powered-off. Leaving instruments on (recording), or keeping the WiFi connections active can quickly drain the battery to the switch-off level. At that point it may not take a long time to reach a state of over-discharge. Keep an eye on the low-battery LED indicator while instruments are in storage.
• When instruments are in storage, always recharge the batteries at least every 6 months.