Yes, talk to Planet ASAP.
Lithium batteries can be extremely dangerous, so have many built-in safeguards. As I understand it, swelling is one of them; when the battery degrades and releases gas, the battery swells to contain it as an alternative to exploding or venting the dangerous gases to the air.
The battery has reached the end of its life, and should be treated with great care:
- Do not charge it.
- Try not to use the device.
- Do not let the battery get punctured or put under mechanical stress.
- Remove the battery if easy to do so, and put it somewhere like a plastic box that would contain any leak or explosion.
- Contact Planet for a replacement.
- If Planet don't take the existing battery, dispose of it appropriately at your local recycling centre. (Do not put it the household trash!)
Sorry if that sounds scary! Chances are, it'll behave itself fine; but there's always a risk with lithium batteries, so it's worth taking some care.
More general info e.g.
here and
here.
