One of the lessons learned after Gerardo's L-39 crash, was the dramatic difference between Li-Po and Li-Ion regarding battery voltage versus remaining capacity.

The easiest way to illustrate this point is with the attached chart.

Basically, at the voltage where a Li-Ion still has about 50% of its capacity remaining, a Li-Po is almost totally drained.
This is mandatory to understand, specially if you use both types of batteries. Checking battery voltage will be useless unless this is fully understood.

Jack

(I am trying to upload the chart with no luck. Let me keep trying)