I don't know what capacity the battery is but its a common issue with low capacity battery packs because the discharge rate is higher per cell the cells don't last as long. So its quite common for cheap or light ebikes which have small capacity battery packs to fail earlier. Made worse of course if you have chosen a proprietary ebike motor system where they charge huge amounts for low capacity battery packs which have proprietary handshaking. The Bosch batteries self-brick if allowed to discharge too far as a way of preventing the batteries being re-celled at the end of life but this can also catch out users who don't keep their battery packs recharged and allow their battery packs to discharge too far. Only really an easy for fair weather or summer only cyclists. I don't know if Fazua batteries are designed to self-brick in the same way but doesn't sound like the cause here.
Generally
Halfords do a fantastic range of bikes which are great value but when it comes to ebikes like most similar importers they use proprietary ebike solutions from one supplier and the Suntour HESC ebike system on many of their ebikes is also problematic compared to open non-proprietary ebike kits where any component can be replaced easily at a much better price.
The law also gives much better flexibility to ebike kits it seems with throttles allowed too;
https://www.pedelecs.co.uk/dft-pedal-cycles-converted-twist-go-exempt-type-approval/
I'm a huge fan of non-proprietary ebike solutions, cheaper, often more reliable, easier to customise and better for the environment. Most ebikes in the world use throttle control too so you control exactly when you need power, no need to bother with power settings or link to cadence or torque.
