Braun ThermoScan Er4 Error — Battery Fix

What it means

Er4 means the battery voltage has dropped below the minimum level required to power the infrared sensor accurately.
The battery icon may have been showing low for some time.
Replace the battery with a fresh 1.5V AA alkaline battery to restore normal operation.

Affected Models

Braun ThermoScan 5 IRT6500
Braun ThermoScan 6 IRT6515
Braun ThermoScan 7 IRT6520
Braun ThermoScan 7 IRT6525

How to Fix It

Locate the battery compartment

The battery compartment is on the back of the ThermoScan handle.
Slide or press the compartment cover in the direction of the arrow to open it.
Remove the old battery

Take out the used 1.5V AA battery.
Note the orientation (+/-) marked inside the compartment before inserting the new battery.
Insert a fresh 1.5V AA alkaline battery

Use a standard 1.5V AA alkaline battery.
Avoid rechargeable NiMH batteries — their lower nominal voltage (1.2V) can cause Er4 even when fully charged.
Insert the battery matching the +/- orientation shown in the compartment.
Close the compartment and test

Replace the battery cover and press the start button to power on the thermometer.
Fit a new lens filter and take a test reading.
Er4 should no longer appear.

Frequently Asked Questions

How long do Braun ThermoScan batteries last?

A standard alkaline AA battery lasts approximately 1,000–3,000 measurements depending on the model.
If you use the thermometer regularly during illness seasons, expect to replace the battery every 6–12 months.

Can I use rechargeable batteries in my Braun ThermoScan?

Braun recommends against rechargeable NiMH batteries.
Their 1.2V output is lower than the 1.5V alkaline standard, which can cause the thermometer to report Er4 prematurely or give inaccurate readings.
Use standard alkaline AA batteries only.