If your Horizon does not charge, you can first check the charger with a Voltmeter. See image below. The charger should output ~54.6V.
If it does not, replace the charger.
Second, you can check for visual damage on the charge port. If it looks burnt or damaged, it needs to be replaced. You can double check for current of the battery on the charge port itself.
CAUTION: Be very careful not to cross the pins while touching the contacts. It will lead to a spark and may damage the battery and lead to injury. If you are unsure, skip this step.
Note the orientation of the port. you want to measure the two pins furthest away from the nudge (circled in red).
If the Voltmeter (set as per above picture to 200V DC) shows any voltage, the charge port is intact. If it shows 0, the battery may be defective, or (more likely), there is a continuity issue in the charge port. Very low voltage, i.e. under 30V, most likely indicates a defective battery.
To replace the charge port, follow the steps in the video: