Many of our consultants who are physically disabled are unable to dress or undress without aid. This suggests that Lithium batteries shouldn’t be built into their wearables as there isn’t an easy way to mitigate against the rare occasion in which the battery catches fire.
These sorts of safety concerns are why the Adafruit Gemma and Flora wearable platforms don’t include LiPo chargers and they encourage the use of NiMH or Alkaline batteries.
SparkFun, on the other hand, builds LiPo chargers into their LilyPad platforms. Presumably, they assume you are going to follow some of the recommendations here: https://learn.sparkfun.com/tutorials/lilypad-basics-powering-your-project.
The safety advice offered in both these sources is inadequate and you should consult a professional engineer and an organization like UL before proceeding: https://www.ul.com/consumer-technology/wp-content/uploads/2017/07/WP_TestingBatterySystemsDesignedForWearableTechnologies_15.pdf
The Flexibility Kit microcontroller baseboard includes neither a charger or the popular JST connector Adafruit and Sparkfun have popularized for battery connections.