I'd like to know what kind of relay I should use to disconnect the load when the battery charge drop to 12V (or any other selected values) and reconnect it once 14.5V (or other) is reached

tnks

 

That decision is based on the actual use of the relay.

You have to find one that will work with the voltage and current load that you are using. What is the maximum voltage and current that will be seen by the load?

Another important factor is how are you going to drive the relay. You will have to have some voltage sensing circuitry for the decision making and also then to drive the relay. What voltage levels exist on the board that you can use to drive a relay?