solenoid takes too much from the battery and the program crashes

If you must use the same solenoid and also the same battery, then try powering up the micro through a schottky diode, and place a large capacitor say, 1000uF on pin Vcc of the micro, ground the negative end of capacitor.

This would prevent the effect of momentary volatge drop on micro.

Or you will have to use separate supply circuits for micro and solenoid.

IA