Questions about Philips Shaver Series 1000

According to the manufacturer, the following heads are suitable for shavers of the 3000 and 1000 series: Philips replacement shaving heads (3 x)

This model definitely has a rechargeable battery, not batteries. Charging takes place via the supplied charging cable with USB plug. No mains adapter is supplied. However, you can use any mobile phone power supply with 5V and USB socket. Incidentally, it is a poor shaver with a weak motor that runs too slowly, presumably to avoid overloading the undersized battery. Shaving performance is moderate, even if it says Philips on it. However, this assessment only relates to the model specified.

There is probably a technical and an economic reason for this: the manufacturer probably wants to ensure that you don't go under water with the device connected and running (electric shock?). It is also good for sales if you have to buy a new device when the battery starts to run down after 3-4 years. Just a guess!