Trex 450XL Pitch curve help

I have joined the wonderful world of RC.
After much deliberation I chose to go the heli route as I have a big
garden
and a park cross the road where I can practice.

I bought a TREX 450XL CCPM kit complete with Align 450L motor and
BL25T ESC.
The radio is a Spektrum DX7.
Batteries are flight power EVO Lite V2 2500mA.
Gyro is the Futaba GY401.
Charger is the Swallow Advanced and I have the flight power V Balance.
I built up the kit and had it set up by one of the experts from the
shop.
I have training gear attached.
Pinion was a 15T but I replaced it with a 13T.
I have been through about 10 battery's so far and I am managing to
hover at
about waist height for a few minutes at a time.

The problem I am finding is I am not getting good battery life.
After 6 or 7 minutes the Trex starts pulsing which I am told is the
sign
that the battery is going flat.
If I let the Trex rest for a few minutes (I assume the battery is
recovering
during this period), I can then take off and hover for a few more
minutes.
After the batteries cool down, the 2 of the 4 leds on the V Balance
fuel
gauge light up for each of the 3 cells in the pack.
It could be my beginner way of flying, it could be not enough pitch ,
new
batteries, training gear weight,
not enough pinion main gear slack etc. etc.

What I would like to do first is change the pitch curve.
It's in the normal position now with values of

L=20.5 (is this too much negative pitch and should I change it to say
50%?)
1=55.5
2=77.0
3=92.5
H=100

Throttle curve

L=0
1=20.5
2=43.0
3=69.5
H=100

Am I on the right track?

What do you suggest as a first step?