Sorry my inexperience, what do you mean with "kick back diode"?
The Duracell that I'm using is a battery of 4.5V. I'm using this because when I bought the waterpump on amazon I read that the DC Voltage required was 5V.
If the problem was the Duracell battery why the MkR Carrier resets? Because I think that the problem is that for some reason (that I don't understand) the Arduino turns off and on in some seconds and thus also the carrier, but during the resetting process the carrier turns on and then turns off again the relays.
Thanks again,
Lorenzo