Glad your enjoying your bike. 🙂
They really are a lot of fun.
The batteries might seem like an expencive purchase, but they will save you a lot of problems.
you have already experienced forgetting to charge, luckily you still managed to make it home without the battery cutting out.
The batteries have an under voltage cutout to save the battery from destroying itself.
When it cuts out the bike loses all power and is impossible to pedal for more than 10 or 20 metres
The battery will come back to life again if disconnected from the bike for a short while and then reconnected. however running the bike again would cut out shortly after and each time it will be damaging the battery. thats why they have under voltage protection.
having 2 batteries increases the lifespan of both batteries as neither battery will ever get too low.
You may not experience these problems as your journey is different to mine.
Thanks for the info on the oxford alarm ive been looking for something like that.