LiPo battery charging efficiency

[Jardar]

Hi

We are looking to have a system where we use the LiPo battery as a emergency/ups type of powersource and as a capacitor bank for high currents draw during network (LTE) connects.. The main power will be delivered from a larger battery, but we are still limmited in battery.
So my questions is about how to optimize powerconsumption with LiPo and charger:

1. What efficiency can we expect from the built-in charger (PySense board)
2. Are there other circuits that are more efficient?
3. What is the best way to implement charging with respect to powersaving (for example only carge when below 50% and charge to 85% instead of 100%)
4. If so are there circuits that do this or does it have to be controlled by software in some way?

[jmarcelino]

@jardar
It's not really possible to give one efficiency figure for the built-in charger because of the many modes and dynamic operation. For full details I refer you to the datasheet of the charger chip used, the BQ24040

http://www.ti.com/lit/ds/symlink/bq24040.pdf