On Wednesday, October 16, 2019 at 12:48:29 PM UTC-4, Dan Marotta wrote:
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

Dan, if you put two 2.5 ohm resistors in parallel the total resistance would be 1.25 ohms. By Ohm's law the current draw with 12 volts would be 9.6 amps. The nominal voltage on LiFeP battery is around 13.6 volts which would be an even higher draw.