what is a soft reset? I want to make my cart last as long as possible and not have to worry about osing my saves if i replace the battery
Have you tested to see if the battery is working as I said in my previous post? As yepi69 says there is no need to replace it if it is working.
As per my first reply, the battery only holds the save until it is written back to the miniSD card when the GBA is turned off and on (or soft reset). After this the save is safely stored on the miniSD and wont be lost even if the battery fails in a few years time.
Soft resetting is resetting the GBA without ever cutting power. Turning the GBA off then back on with the power switch is a 'hard reset' as it turns power off completely.
The EZ-Flash client can add a 'soft reset' key combination to games, so that when you press the combination of keys (L+A+B+Down) while playing a game, it resets back to the ez-flash IV menu without ever cutting power. This allows the save to be written back to the miniSD card even if the battery in the EZ-flash is flat, as the console is powering the cartridge the whole time.
Test it out and see if the battery is working, I think you're worrying about issues before you even have them yet
Read the links from my first reply, test, google any issues. If you get stuck let us know and someone will be able to help.