What Battery for RTC VBAT?

It took a lot of hunting in this forum to figure out how to access the VBAT pin on my Hydra+ and Spider I. I now understand the secret is the Z socket and a G-Plug. But I am still unclear about the battery voltage needed.

There was a comment from one user that for the Spider, a 3V coin cell would work just fine. But another discovered that 3V would not work for the Hydra and 1V5 was found to work (supposedly a LR44 Button cell or maybe even a single AAA alkaline).

So what is the real spec? I would like to use the same solution for both boards - would 1.5 V work for both?

As for my Cerberus, I think I will just go with one of the external modules, from DFRobot IIRC.


All devices would work fine at 3V. However, hydra is an exception where it needs a lower voltage. I forgot what the limits were.

Exact details on what would be the needed voltage be is found in the processors’ datasheet.