So a couple of questions: how do you know it 'fused out'?
Did you charge the accumulators? Did you double-check polarity?
It might be that the controller is in a fault mode (does it have a status LED?).
Also do you realize that SLA batteries are not +/- 10% - they can go well below rated voltage if discharged. The spec for the controller says '9A max' but its not clear if that is the maximum it will pull or whether its the maximum it can tolerate (former more likely). 7Ah batteries can probably deliver several hundred amps BTW.
You might just have a rogue controller, but its worth checking it hasn't just cut out because its detected a fault condition - double check all connections.