Check the connecting plugs/sockets are all pushed home firmly, which im sure you have done..
Check the manual for first time running instructions, many halfords bikes employ direct communication with the battery and controller, this may require a full charge of the battery, for initialisation???? - no experience of your bike, so clutching at proverbial straws)
anything more invasive could affect your warranty..
If the 80% charge is deduced from battery leds?? thats a 'rough guess based on an estimate based on an approximation', so just an indicator.. give it a full charge, it may be weak and pulled to low voltage on connection to the bike..
The battery comms issue however is something which if applicable to your bike may be something you want to bear in mind when taking the bike back to halfords for repair/replacement/return..
Edit* Welcome to the forum btw..