A ballast for outdoor signage of a commercial building should have a relatively long lifespan. In fact, you could expect to get up to 20 years out of an electrical ballast. Keep in mind that environmental factors may play a role in how long a ballast will last. If you live in an area with harsh winters, you should expect a shortened lifespan for your ballast. Thankfully replacing a ballast is not a major electrical issue and is something that can be replaced.