Battery light permanently on bright means slip ring / brush failure, or field winding failure or regulator failure or fan belt problem. It can also be caused if the main power feed from the alternator to the battery is broken or sub standard as the alternator regulator will go into a forced shutdown, ditto with a battery which has problems.
Check the fan belt first as that's the easy one. Take drivers seat off and fire up the motor, check for squeaks. If your battery is aged and flattening itself the alternator will have to work extra hard initially and will be prone to slipping if loose, if there's damp weather etc. etc. If you can hear squeaks, sprinkle a bit of talc on the belt when the engine is off to see if there's an improvement.
The next one to check is connections. The main power feed from the alternator to the battery must be perfect - that includes any ground connections, so please take everything off the earth straps, battery leads and bolt on connection to the alternator and make sure they are spotlessly clean.
Third thing to look at is the battery itself. After 6 years, it's probably had its best years
Do you have a charger? Leave it on a slow overnight charge and then fire the van up. Does the red light go off once the engine fires up?
Other than that, it's likely to be a fault within the alternator itself but check the cheap things above first before coughing up wads of cash.
Battery voltages vary with temperature, but in the current cool climate look for near 13 volts from the battery when it has been sitting round unused for an hour or more with the engine not running. On a fast idle, expect to see figures over 14 if it's being charged correctly.
