I have atleast 6 apps running 24x7 on my 5230 i.e from boot to shutdown (set to autostart):
An SMS Blocker
A Call blocker
A Call Recorder
JBakTaskMan
A Profile Changer
PocketSensor (Proximity Sensor)
Also using my own flash homescreen with time display in seconds with 1fps frame rate.
+ Moderate use like playing a game, some video clips, radio, music etc for a couple of hours on an 8GB microsdhc.
I charge it once everyday with almost 40-50% battery remaining.
The BL-5J battery 1320mAh which comes with the 5230 is quite robust and should last you atleast a day even with multiple apps and heavy use. Standby times are a good 2-3 days for the average user.
Even with GPS and internet use, I have never had to recharge the battery more than once any day.
Also, my custom firmware has the cpu running at max cycle rate and is optimized for performance and not battery.
A simple tip would be to disable the Network mode from Dual Mode to GSM only (disable 3G/UMTS if you don't use it) and adjust the backlight optimally.
PocketSensor is a good app to replace the keylock and save battery life too.