In Car Solar mp3 charger

 

Hi, I have a cheap mp3 player in my car that runs off a 1.5v aaa
battery.
I have to change the battery once twice a week as I forget to turn the
thing off as it is plugged into the tape slot.
My plan is build a circuit that will trickle charge a Ni-MH battery via
a solar cell and power the mp3 player during daylight, and the battery
will power it in bad light/ darkness.

This is a very cheap mp3 player and the only power connection it will
take is off the battery terminals.

I have a 2.5v solar cell on the way from e-bay, and I know  I need a
diode to stop the batterry discharging via the solar cell, and possible
a voltage regulator so as not to overload the mp3 player.

Any other suggestions to improve on this?