In the Antares I'd expect to get to ~2500 feet AGL if the
ground temperature was 37C (100F). This at Sisteron at 1770
feet; so not a lot different to El Tiro altitude, this assumes that
the batteries/electronics are cool at the start. On my A/C the
climb limit would be the engine temperature not the battery
temperature. After such a climb I'd expect 50-60% battery
charge remaining so you'd certainly get a healthy climb at the
end of the day.
A Honda generator is a very non ideal way to charge the
batteries, perhaps it wasn't powerful enough? Plugged into the
mains (a 230 volt 16A supply) it rarely takes 7 hours to fully
charge.
As I've said before you cannot fly it like a DG800 but not many
pilots go from Antares20E to DG800.
And before the DG owners pass comment I did own a DG808C
for several years.
Dave Walsh