Batteries for the S1 and the remote control should be charged with the proprietary S1 charger only. The recommended USB power output for charging is: 5V/2A (like an iPad charger). If you're charging with only 1 battery or only the remote control, 5V/1A USB power output would be recommended. The charger may produce a beeping noise if it's charged with the wrong USB power output.
If the battery swells up, please dispose it properly*. If the battery swells in the S1 and you are not able to remove the battery, do not attempt to remove the battery! As this will pose many hazards such as fire and explosion. Please contact support immediately: https://removu.zendesk.com/hc/en-us/requests/new
Do not drop, disassemble, open, crush, bend, deform, puncture, shred, microwave, incinerate or paint the battery. Do not insert foreign objects into the battery terminals. Do not use the battery if it appears damaged. Disassembling or puncturing the battery can cause explosion or fire.
* Most rechargeable Li-Polymer batteries are classified as non-hazardous waste and are safe for disposal in the normal municipal waste stream. Many localities have laws in place requiring battery recycling. Check your local laws to make sure that you can dispose of rechargeable batteries in your regular trash. To safely dispose of Li-Polymer batteries, protect terminals from exposure to other metal with packing, masking or electrical tape so they do not cause a fire while being transported. Never dispose of a battery in a fire because it may explode.