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Device battery FAQ

On charging and predicting your TRMNL's energy.

Ryan avatar
Written by Ryan
Updated over a week ago

While logged into TRMNL you can see WiFi + battery strength from your device picker or all devices view:

Calculating remaining battery power is a simple equation, but it becomes less reliable as energy is drained and playlist refresh rates change.

Low battery notification

When your TRMNL device has < 10% energy remaining, you'll be notified by the following screen on your display:

In the future you may be able to customize this screen. ;)

Charging your TRMNL

There are 2 battery options, 1800mAh (default) and 2500mAh (upgraded).

Assuming 0% energy:

  • 1800mAh - 3.5 hours to full charge

  • 2500mAh - 5 hours to full charge

When a TRMNL is plugged in to charge, you may notice its reported battery power seems to fully restore within minutes:

However this is not necessarily true. As of this writing, TRMNL's web interface does not differentiate between "now charging" versus "fully charged."

Therefore, whenever you see the low battery screen, we suggest plugging in your TRMNL for at least a couple hours.

Percent charged versus voltage

The X% charge value in your TRMNL account is approximated as follows:

def percent_charged
self.battery_voltage ||= 100 # assume full charge if device not yet set up
pct_charged = ((battery_voltage - 3) / 0.012).round(2)

case pct_charged
when 90..1000000 # account for '100+' charge, ie plugged in
100.0
when 10..90
pct_charged.round(2)
when -1000000..10
1.0
end
end

If you instead prefer to know your device's last reported voltage, just hover the battery icon(s) for a read out:

Understanding power consumption

One refresh cycle takes 32.8mA over a period of 24s. In this time the device will ping the TRMNL server, download an image, and refresh the display.

If there is no need to download and refresh the display with new image content -- for example if an image is not returned, or the returned image matches what is currently displayed -- power consumption will be around 20% of the above calculation.

For more comprehensive details on TRMNL device power consumption, see here:

Determining your battery type

TRMNL devices offer multiple battery size options. If you are not sure which one came in your device, or simply want to verify:

  1. Disassemble your device (unless it is a clear case)

  2. Compare your battery's shape and size to the photo below

  3. For further confirmation, detach the battery (will require new tape) and look on the under side, which will show the mAh value

Top: 1800mAh
Bottom: 2500mAh
​

TRMNL 1800mAh, 2500mAh batteries
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