[raymo]

When the focuser reaches the fully in/out position the focuser knob should
barely slow down, let alone stop, so only two likely possibilities:
Battery low, if yours suffers from the problem I mentioned before, even
leaving the battery installed overnight is enough to partially or completely
flatten it, so worth checking the battery, or trying another one that you know
is good.
Motor, or motor controller circuitry is faulty.

If the motor is freed from driving anything, does it go through the changes
in speed seamlessly when you rotate the speed control knob, and it should
feel powerful if you try to stop it turning by hand when running at high speed.
If you can easily take the focuser through its range of movement using the knobs when the motor is not attached to it, you can forget the focuser as being the cause of your problem.
The battery should last for ages, so if it turns out that your new battery
is already seriously low, it looks like you have the problem I mentioned
before, and will have to put an on/off switch into it, like I did, or remove
the battery between each viewing session, or return it for a refund.
raymo