Ian wrote:

Asuming a 15Ah battery, you are using 15 amps to power your systems. That
is an awful lot. Did you shut off the alternater field?
The usual FI 13B in a plane will go for about 3 to 4 hours.

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I measured the amps to run the engine as 7.8 amps. Hard to believe a FI
13B can run 4 hours. Tracy seemed surprised that it only need 7.8 amps. A
15 amp-hour battery will not deliver 15 at that load. If you read the
fine print, the rating is at a couple of amps load. Do not know when this
battery would drop off like a rock at some voltage. When I ran it with a
ground test at 12 amps, it bombed at 11 volts and 12 amp hours.

Bernie, a neophyte on electrical stuff, but this is what I have observed