...Goes good for about the first 3 seconds. Had 2 of the batteries explode and the other 2 weren't far from exploding...
This really doesn't make sense - unless there is a direct short the packs can't get hot enough to explode in 3 seconds of running. The OP needs to tell us more: exact boat and size, the ESC, the prop, how the packs are charged and exactly how the boat is run (time, throttle position, etc.). Some ESCs do not have programmable low voltage cutoffs so using a timer is a good suggestion.
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