Batteries in parallel

I was interested to spot batteries in parallel in this LED garden light. It is designed to glow at night, so the solar panel cannot power the LED directly. During the day sunlight causes the solar panel to charge the lower battery. That then discharges at night through the LED. However, it might be that there is not enough charge on a dull day so the second non-rechargeable battery is there for when the rechargeable one has emptied itself. It doesn't add to the total output p.d. but is a substitute hence they are wired in parallel.