2G vs 3G mode. How much battery do you safe if you use 2G when you don't need phone?

[Nejco]

And cellural data is off. I'm not looking for numbers here, I'm just wonering if it's worth switching to 2G to save energy or is difference nearly 0%

[Bad 💀 Motha]

You don't need ANY "G" Cell Services enabled (aka Mobile Data) when you want to save battery, while still allowing for Voice Calling & Texts (inbound / outgoing)

You only need Mobile Data (or WiFi) for Updating Apps, connecting to Online based Apps, or general Internet/Web access.

Switching Mobile Data Modes really won't change the power needs; a slow rate will just be slower I/O meaning data will take longer to download/upload due to the slower max bandwidth it can use.

Only ways to really save alot more power is turn off Mobile Data and/or WiFi.
Using a decent app that can force-closed background apps is also a good way to help save battery power.

If you want to help make the battery last long; or charge faster; Enable Airplane Mode. However, when Airplane Mode is Enabled; nothing data wise will be allowed; not even Voice Calls/Texts.

[Nejco]

I'm asking if 3G when celluar data is off consumes more energy than 2G when it's off too

[Bad 💀 Motha]

If Mobile Data is turned off/disabled then all of those "G" modes are off.

When on, they generally use the same amount of power; they just differ in max capable bandwidth.