Although the battery charges ok while idling, it's not getting enough charge to 'maintain' a good voltage overnight. You can try charging the battery with a mains powered battery charger instead. It will take several hours. That should give you a few weeks without the 'remote features disabled' message. If it doesn't, you may have a fault with the battery, BMS or another module that would need to be repaired under warranty.
Ford shouldn't be suggesting yearly servicing for a Focus MHEV in the UK. It's 2 years or 18k miles. However, many Ford dealerships send the same automated email to every customer, suggesting that they need a yearly service. I was told this was an 'oversight' by my local dealership when I complained about it (especially where they suggested warranty would be void without a yearly service!) but sadly a year later they had still not rectified this 'oversight'. I wonder how many customers are being ripped off by this...
It is worth noting that most Ford dealerships offer free breakdown cover with a service. That only lasts one year, so will expire if you don't have a yearly service with them. However, you can purchase your own breakdown cover.