When a vacuum cleaner battery is worn out can the battery be replaced?

It is possible to replace the battery in a vacuum, but this may prove to be a difficult and expensive project. Some vacuums have battery packs that can be swapped out, like the Dyson stick or the iRobot. Others have battery packs that must be made up by connecting individual batteries together to obtain the finished battery pack. Rechargeable batteries are expensive, and it might cost more to replace a battery pack in a simple cordless hand vacuum than to replace the machine.