Battery life is usually measured in years and charging cycles rather than a fixed mileage, and gradual loss of usable capacity is more common than sudden failure.
Check the manufacturer warranty
Battery warranties vary. Look at the time, mileage and minimum-capacity terms for the exact vehicle rather than assuming all electric vans are covered in the same way.
Duty cycle matters
Frequent rapid charging, high temperatures, heavy use and long periods at very high or low charge can influence battery ageing, although modern battery management systems reduce risk.
Range loss may matter before battery failure
A van can remain perfectly usable even after some capacity loss. The question is whether the remaining real-world range still suits its route.
Consider battery health when buying used
For a used electric van, battery condition and charging history can be more informative than age alone. Ask for available battery-health information.