If there is an issue where the battery of a 3i Plus is not charging while it is installed inside the device, the first step is to ensure that correct charging cable is used.
3iPlus is supplied with 2 sets of cable.They are the data cable & power cable.Both appear identical, however the power cable is shorter & has a black sticker with red text on it.
This is a special cable & the battery of a 3iPlus can be charged by only using this power cable.