The low-cost battery thermal safety system


ReliaTherm is a cost-effective temperature monitoring system for large battery installations.

  • Monitors individual unit temperatures for thermal runaway conditions
  • Enables compliance with US IFC608.3 (2010)
  • Simple fail-safe, isolated change-over relay alarm contacts (2)
  • Bright LEDs pinpoint individual over-temperature cells
  • Fast one-wire acid and gas tight connections
  • Sensor circuit break detection
  • Power supply failure warning (fail-safe)

ReliaTherm Sensor

Thermal Runaway

The Problem

Operating a standby battery in higher temperatures than specified can seriously shorten its life. Every 10°C above 25°C (77°F) reduces the service life of the battery by 50%.

Additionally, it is a potentially serious condition, often caused by either:

  • a fault condition within the battery cells leading to higher cell temperature
  • a higher than recommended ambient temperature.

These can promote a fault within a cell, leading to a high current draw and thus higher temperatures – and so on. It is an exponential ‘positive feedback’ progression of increasing temperature often leading to explosion. In the United States, US IFC608.3 (2010) requires that if a sealed battery (or batteries) operated in a single premises contains over 50 gallons of acid the proprietor must install measures to prevent thermal runaway.

While US IFC608.3 is intended to prevent a catastrophic explosion damaging the surrounding environment, batteries with smaller total amounts of acid should also be protected as they are just as vulnerable to thermal runaway as larger installations.

Our Solution

The ReliaTherm system is a dependable low-cost way of protecting your battery against over-temperature and thermal runaway conditions. Volt-free alarm relay contacts warn of critical conditions, and can be used to take action to prevent the condition from continuing.


Each thermal sensor is sealed to IP67 (liquid and dust proof) and the special gel-filled connectors provided are also sealed against acid ingress, dust and gasses. The ‘cold-weld’ connections made by the IDC connectors are rated by Lloyds as the equivalent of a soldered connection for vibration and adverse conditions.

Simple installation

Individual sensors are quickly and securely attached to each battery cell and connected in series; the cables do not require stripping and a pair of side-cutting pliers are all that is needed to trim the cables to the required length for a neat and unobtrusive sensor installation. Interconnections typically take less than 20 seconds each.

Fast installation

Longer interconnections, such as shelf to shelf and rack to rack are simple to accommodate. Cable lengths, within reason, are not sensitive. Sensor installation for a 40-unit (cell) battery will typically take less than an hour.


Several different sensors on batteries in the vicinity of each other may be connected in series to the same monitor. In excess of 100 sensors can be connected to a single monitor. As the system is electrically isolated from the battery, voltages and polarities are not an issue. Sensor modules are not polarity-sensitive and may be connected either way round.

Fault identification

In the event of one or more cells exceeding critical temperature the monitor warning relay activates and the warning LED on the monitor is illuminated; at the same time a bright LED flashes on the sensor attached to the over-temperature battery cell, indicating the source of the fault.

Critical warning relays

Should more than 4 cells exceed critical temperature, the system-critical alarm relay activates, warning of a serious situation in the battery as a whole. Up to 12 sensor LEDs can be indicate simultaneously.

System state

Additional LEDs warn of power failure and a break in the sensor circuit.