Charging lithium batteries while supplying power to load
Your charger must have a power capacity much greater than the worst case load so that charging occurs but at a slower rate. The mobile senses its own current and voltage to prevent over charge durations &gt;3.8V/cell at CV=4.2/ cell.
If your supply was maxed out and fully loaded then the battery charger would take too long during CV mode towards CC /20 to CC/5 cutoff.