Type of battery for RTC module

Hi,

I got a bunch of DS3221 mini RTC boards for use with the Arduino, unfortunately I did not notice the small print where they say they came without battery.
rtc4pi.PNG
I can’t even find out the battery model. I guess that any 3v battery would do but I’d like to get one with pre-soldered contacts that fits that small space, just like the one in the pics.
If you only know the battery model, please tell me, that would help.

Thank you.

Any CR will work. Find out what size should fit.

CR2025 means its 2.5mm thick, and ø20mm
CR1025 means its 2.5mm thick, and ø10mm
and so on..

Allmost every CR battery is available with solder lips

rtc4pi.PNG

Those are RaspberryPi modules. Meant to plug directly into the double row i/o connector.

It seems some the Chinese sellers stopped installing batteries in consideration of the lithium battery ban in air cargo. Most of the rtc3231 boards used rechargeable coin cells charged by the battery mangement circuit of the '3231. Non-rechargeable cells work fine as well, just be sure to off the charger in the library code.

avr_fred:
Those are RaspberryPi modules. Meant to plug directly into the double row i/o connector.

It seems some the Chinese sellers stopped installing batteries in consideration of the lithium battery ban in air cargo. Most of the rtc3231 boards used rechargeable coin cells charged by the battery mangement circuit of the '3231. Non-rechargeable cells work fine as well, just be sure to off the charger in the library code.

They were made thinking about the Pi, but as they work well with 5V they are quite popular with the arduino due to is size. You just have to wire the i2c bus to the correct pins instead of sticking it in the Pi GPIO header.
I have it working well with a Nano, and are planning to use it with a esp8266, but I DO need a battery.
I think (but I'm not sure) that these Pi boards do not support rechargeble batteries, I have a larger RTC module that comes with the rechargable version of the CR2032 (LIR something) but it's about twice the size of this one.
I'm sure someone must know the model of the battery, but I've been searching for days without success.
Thank you

ocsav:
planning to use it with a esp8266

No need. Unless the esp is likely to spend time away from a wifi signal. But otherwise it can keep perfect time by itself, syncing up with an NTP time server on startup and perhaps once every 24hrs after.

CR1025

avr_fred:
Those are RaspberryPi modules. Meant to plug directly into the double row i/o connector.

It seems some the Chinese sellers stopped installing batteries in consideration of the lithium battery ban in air cargo. Most of the rtc3231 boards used rechargeable coin cells charged by the battery mangement circuit of the '3231. Non-rechargeable cells work fine as well, just be sure to off the charger in the library code.

The DS3231 IC has no battery charge circuitry. Modules that charge do it externally, not under software control. Those modules require hardware changes to disable the charge circuit.

I spoke without checking the datasheet, the DS3231 does not support rechargeable batteries directly, several other Dallas/Maxim RTC chips do. That's what happens when think you know something and you don't check yourself...

Go with with a non-rechargeable battery. If you cannot find the CR1025 with tabs for a direct mount, a 2032 in an external holder with flying leads would do in a pinch.

If you have a "Batteries and Bulbs" near you, they'll weld tabs on the cells for you for a very nominal fee.

billhowl:
CR1025

thank you.

avr_fred:
I spoke without checking the datasheet, the DS3231 does not support rechargeable batteries directly, several other Dallas/Maxim RTC chips do. That's what happens when think you know something and you don't check yourself...

Go with with a non-rechargeable battery. If you cannot find the CR1025 with tabs for a direct mount, a 2032 in an external holder with flying leads would do in a pinch.

If you have a "Batteries and Bulbs" near you, they'll weld tabs on the cells for you for a very nominal fee.

I might have to go for the external holder solution, CR1025 with tabs looks to be quite rare.
I'm affraid that Batteries + Bulbs does not exist on my country.
I might try to solder some solid wires using liquid flux.
Thanks for your help.

I might try to solder some solid wires using liquid flux

Do not attempt this!!! The cells have no mass and a solding iron can and will impart enough heat to risk an explosion. Spot welding is the only way small coin cell batteries can be terminated safely.

Molden solder flying everywhere is not pleasant thing. There is a YouTube video showing a CR2032 exploding with the heat from a soldering iron. Google it along with "soldering coin cell battery".