By The Numbers: LiFe batteries

Lithium Iron Phosphate (aka LiFe, LiFePo, LiFePo4) batteries are most often used in RCLand for transmitters.  They're safer than LiPo, since they don't emit oxygen during rapid breakdown leading to combustion.  Lots of chemical detail on wikipedia.

Here's the model that fits into the Turnigy 9X transmitter.  Use the servo-style connector to plug it in.  Note that there are two ways to plug it in: only one of them works; the other doesn't do anything.

Charge Levels

 1S   3S

3.3   9.9  nominal voltage

2.8   8.4  minimal discharge

3.6  10.8  maximum voltage

Charging

You need to set your charge into LiFe mode.  Don't charge in LiPo mode. Bruce has a video here that explains how to do this on a standard 4-button charger. Here's the tldr for a typical 1500 mAh 3S:

Save Data / 01 / LiFe / 9.9 / 1500 / (hold start) / 1.0 / 9.9 / (hold start)
Save Data / pgm number / LiFe / voltage / mah / (hold start) / charge current / voltage / (hold start)