> (...I'm fairly certain the constant voltage is for when the battery is low) Backwards. When the cell is low, the charging is at a constant current. The curre

> (...I'm fairly certain the constant voltage is for when the battery is low) Backwards. When the cell is low, the charging is at a constant current. The current is limited to whatever is deemed safe for the battery. Once the battery has charged to 80% or so, then the voltage will have reached the top, and any attempt to maintain the current will over-volt the cells. So the current is allowed to taper off as the voltage is held constant. For a single cell, that means the charger will apply whatever voltage is needed to deliver, say, 1 amp. Then when the voltage hits the 4.2V ceiling, it will stay there as the current naturally decays. A 100% charge is declared when the current falls below some threshold, like 50mA.