Yes. All 3DS and DS cartridges (except those with broken ROM chips) work on the latest firmware. The update does not block original games.

There is no universal answer. Your decision depends on your goals.

The version will be displayed as a string (e.g., Ver. 11.17.0-50U ). stands for Americas. E stands for Europe. J stands for Japan. 🚀 How to Update Your System

No. Later versions (11.x) have no measurable impact on battery versus 9.x. Battery degradation is purely hardware-related.