If your iPhone’s battery is on the fritz or doesn't hold a charge as long as it should, it would typically cost about $79 to get it replaced at an Apple store. As Geek.com helpfully points out, though, an ongoing Apple deal lets you snag a new battery for just $29.

The battery replacement program applies to the iPhone 6 and later models. This includes out-of-warranty iPhones like the SE, 6 Plus, 6s, 6s Plus, 7, 7 Plus, 8, 8 Plus, and X.

The offer expires on December 31, 2018, so if you’re having battery issues, you’ll want to make an appointment at your local Apple Store’s Genius Bar as soon as possible. December 31 is also the deadline to contact Apple for a $50 credit if you bought an out-of-warranty battery for the iPhone 6 or a later model between January 1, 2017 and December 28, 2017.

If you aren’t sure whether your iPhone’s battery is still viable, go to your phone’s Settings and select Battery, then Battery Health. This will tell you whether your phone is working at maximum capacity. Brand new phones should function at 100 percent capacity, while lower percentages indicate it’s not holding a charge as long as it once did. Anything below 80 percent is cause for concern.

“A normal battery is designed to retain up to 80 percent of its original capacity at 500 complete charge cycles when operating under normal conditions,” Apple states. “The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge.”

If you plan on keeping your current phone for a while, it might not be a bad idea to take advantage of the battery replacement deal. Doing so would prolong your phone’s usefulness and may prevent future problems, Geek.com points out.

[h/t Geek.com]