It is normal behavior that the HyperJuice can get warm. Especially when charging multiple devices, a high-powered device, charging devices that have low percentage and other configurations, but it is safe.
Multiple Safety Protection
The HyperJuice charger has protection to shutdown the unit if it experiences any signs of over-current, over-voltage, over-temperature and short circuit protection.
Maximum Operating Temperature
The HyperJuice 87W charger can go up to, but NOT exceed 140°F/60°C.