Adelaide South Australia
I've got 4 Astro 109s and use the ThunderPower 5 and 10 cell balancers. Used them for 2 years (approx) and never had any problems with them shutting down like you describe. From the stories here and elsewhere, the 109 has been involved in most of the LiPo fires but, in my opinion, the fires have nearly always been due to the inattention of the operator. Make absolutely sure that the cell count is correct as it goes into phase 2 of the charge and you should be OK.