OtterBox says it has detected an issue with early units of its OtterSpot system. The company released the wireless charging batteries back in August 2019. It says that units that were manufactured between July and August that year may swell “under multi-stack and higher temperature conditions.”

As yet, no injuries have been reported due to the issue, OtterBox told The Verge. The company is contacting customers it knows bought an affected unit, but if you have any OtterSpot battery packs, it’s worth checking the serial numbers. If the number starts with 229, 250 or 259, the unit could be affected by this issue and it’s worth calling customer service at 1-855-688-7269. OtterBox says it will replace potentially defective batteries at no cost.

The conditions under which affected units could swell may not be rare. One of the key selling points of OtterSpot is that it comprises a base unit and stackable battery packs, which you can use to wirelessly charge devices on the go. Up to three packs can be charged on the base simultaneously. You can juice up a Qi-compatible device at the same time by placing it on top.

The issue might not affect too many units, since OtterBox says it only had a limited quantity at launch. Still, if you have one, it’s worth checking the serial number just in case.