Sounds like poor quality packs are being used. Brushless power requires top quality packs as the cheaper packs can not provide the current demanded by the motor. When the motor demands this high current the pack can not provide it creating a large voltage drop and tripping the LVC or stalling the ESC.

This issue is extremely common for new boaters to the brushless world. If you do a search there will be several others with this issue.

LiPo is highly recommended. Or at worst case use only IB or GP cells of 4200mAh or higher.

In a couple weeks the canadian nationals fast electric race will be held in London. Check out RCU's event listings if you are interested.

Ryan