There is no single voltage threshold at which this type of battery (Li-SOCl₂ chemistry) should be replaced. These are professional-grade batteries designed for demanding outdoor applications. They have extremely high energy density, operate across a wide temperature range, and are very durable. However, they are also notoriously difficult to assess based on voltage alone.

Unlike most battery chemistries, Li-SOCl₂ batteries maintain a fairly constant voltage for most of their life and then drop rapidly at end-of-life. This means the voltage does not gradually decrease in a predictable way as capacity is used. Instead, it stays relatively flat and then collapses suddenly.

On top of that, the voltage reading is strongly influenced by:

• Ambient temperature

• Current draw

• How long the battery has been idle

Because of these factors, a single voltage reading cannot reliably indicate remaining capacity.

For example, on your Zenseio Dashboard, you can see the battery voltage (green) and ambient temperature (purple) over the past year. Daily voltage swings are caused by day/night temperature changes. Last summer, the voltage was higher simply because temperatures were about 45°F warmer. Seasonal temperature differences alone can shift the voltage enough to make direct comparisons misleading.

In theory, remaining capacity can be inferred by comparing voltage behavior under similar temperature conditions, but in practice this is difficult because those conditions are rarely identical.

Practical guidance for CSMP devices

Instead of relying on a fixed voltage number, we use behavioral indicators:

You should plan to replace the battery when, at similar temperatures to last year, you observe:

• Much larger daily voltage fluctuations, or

• Consistently lower voltages than before

As a general rule of thumb, CSMP batteries typically last 1–2 seasons, depending on:

• Active season length

• Transmission interval

• Probe type

• Cellular signal quality

It’s important to be cautious: the cellular radio module does not tolerate abrupt power loss well. A severely weakened battery can cause sudden brownouts that may permanently damage the radio. The manufacturer (MultiTech) does not cover this type of damage under warranty, as it is considered a usage-related issue rather than a defect.

Practical guidance for LSMP devices

For LSMP devices, battery life is typically several years. There is no radio module sensitivity issue like with CSMP, so these batteries can safely be used all the way to end-of-life without risk of device damage.

We now offer an improved battery model with an additional “booster” cell. This design stabilizes voltage across temperature changes and adds capacity. As a result, the voltage remains much closer to the nominal 3.6V even in cold conditions, allowing the device to shut down in a more controlled and safer way. This leads to longer battery life and better reliability.

If you prefer not to deal with battery replacements at all, we also offer a solar charging kit that uses a rechargeable battery charged by a small solar panel.