Andy maybe your hobbyking batteries are the issue, and perhaps you need to balance up individual cells within the packs.
see: https://youtu.be/wIbHLacozFo
Fabulous video.
I had accidentally managed to mix my 2 sets of hobbyking saddles up and both are now out of balance. When I charge (always balance) I can only get to ~8.2v before the timer cuts out on the charger. I will have a got at this, although I presume that I could simply do a 1s standard charge without the need for the lead as saddles have the 4mm bullets per cell?
__________________
I've got Araldite and a Swiss Army Knife - what more do I need?
Yokomo YZ-2
No 4WD because nothing lives up to my original Optima. Until now maybe?...