LiFePO4 Batteries Discharge Fast After Recharge
LiFePO4 cells have a very flat charging voltage curve that doesn't peak until just before full charge. When charging a 400mA pack at 10mA it may stay below 3.5V for 30 hours or more.

As a result of the sharp voltage peak at end of charge, a small imbalance can cause large voltage variations between cells in series. An aggressive balancing circuit will fix this problem, but may consume some current itself (which could be significant at low charge rates).        

How to charge Lithium Iron Phosphate