A Different Battery Question

I've been using a 20 AH LiFePO4 battery as a backup in the Stemme. It's
portable and secured behind the passenger seat.Â* I charge it outside of
the aircraft.Â* When used, it is connected through an DPST switch (only
one half used) and switches the tail battery out of the system as it's
switched in.

The problem:Â* Even when fully charged it comes on line at around 11.4
volts or below and, if I key the radio, the radio display flashes and
the vario gives a Low Voltage warning.Â* When the tail battery is at 11.4
volts (it's an SLA battery), the radio works fine.

I've tested the lithium battery using a pair of 2.5 ohm power resistors
in parallel and measuring with a Watts Up power meter and it seems to
perform just fine, starting with voltage in the high 13s.Â* I ran it for
several hours that way, burning up about 15 amp hours without the
voltage ever dropping below the mid 12s.

Any ideas?Â* Everything seems to work just fine except for the low
voltage as measured at my ClearNav and at the Dynon D10a.Â* I'm using
good quality Tefzel wire of sufficient diameter, Power Pole connectors,
and the battery is properly fused.Â* I'm at a loss.
--
Dan, 5J