Charge it up independently so its fully charged then use to move the van , when it gives up ,just measure the voltage if it below 12.6V it's a fair chance it's had it .It's not precise but Spending about £100 on a new one will give you piece of mind.Then you have think why the first battery failed. Do you have solar panels fitted or do you regularly remove the battery when in storage , particularly in winter, and keep warm and charge it up ( lead acid batteries don't survive well if slightly flat and left in the cold).