lipo question

I've charge my 5000mAh, 3s TP pack yesterday, but only put 60% in it for winter storage, and stop it at 11.85 volts.
Tonight, i've try my e-logger for the first time, and when i look at the graph, my pack voltage drop a 9.6 volts under hard acceleration. Is it normal that the pack drop as low for a high quality pack? Is this just because the pack was not fully charge at first??

My setup is TP 5000mAh, 3s pack, Neu 1509, 2.5d on slash geared for 43 m/h.

The max amps i've read is 64 amps on hard acceleration, not too bad