I agree with RC; not only are they expensive, but also quite rugged. I would do some probing and measuring before ruling anything out.
Are there signals on the gates? Is the micro-controller running?
You haven't mentioned batteries; what kind of battery packs are there, and can you confirm that they are being charged?
You did say there is an alarm. This could mean the unit is finding something it does not like: low battery, over or under current or voltage, thermal issues....