Frustration and Invention

I have a few DS3231 Real Time Clock (RTC) modules with battery backup where the battery has fully discharged. This battery is not rechargeable and is soldered onto the PCB.

Finding a way to change these over was a frustrating experience and prompted me to explore and invent a better way.

The compact DS3231 I use in my projects (shown on the right) have a CR927 battery with solder tabs. These batteries last for years but when they are discharged, the time and configured clock settings are lost when the module is powered down.

These tabbed batteries only seem to be available in bulk quantities from standard online sources (minimum order 100+). A standard CR927 cell, on the other hand, is easily sourced.

So I ordered a few of the standard types with the intention creating my own ‘tabs’ by soldering wire to them. Simple idea, except that the batteries don’t like to be heated with the soldering iron, emitting smoke and becoming damaged goods. I needed to find a different way to attach wire – without heat.

The solution I came up with is a small 3D printed cell holder with wire contacts on either side of the cell.

The cell holder (modelled in Fusion360 and shown above) holds the cell in a small insulated compartment. The back of the holder allows 1mm diameter wire to poke through. The wire inside the holder is shaped into a small loop (below) and wedged against the cell by the sides of the holder.

The whole assembly can be used to replace the tabbed battery, with the added bonus future replacements are a matter of sliding out the old battery and inserting a new one.

The Fusion360 module is parametrised and should be easily adaptable to other battery sizes if needed. The model is available from this Dropbox link.