Here is an example, however the constant current draw to operate the relay may be an issue. (and you'll have to select components and values to suit the voltage and current).
Nevertheless, this circuit does have some useful properties that you'll need:
1) it has hysteresis. The voltage will rise once the load has been removed, and the last thing you want is the load turning on and off and on and of and on and off... when the battery gets close to flat. You want it to turn off and stay off until the battery is significantly charged (so the voltage which turns it on needs to be somewhat higher than the voltage which turns it off.)
2) it switches rapidly. A 10A load from a 20V battery is 200W. Unless the switching device turns on and off quickly you will release lots of heat and possibly destroy the switching device (many low voltage cut-out circuits do NOT switch rapidly and they would likely fail in your application). Having said that, this circuit relies on the relay dropping out, and that's not going to provide an especially fast turn on or off so the relay contacts need to be rated for a significant current.
3) it needs to be able to withstand 44V (or even higher). Many electronic devices used in similar circuits will have a maximum voltage well under 45V.
Given your load is several amps, the current required to operate the relay may be an acceptably small additional current. You probably need a 24 or 36 volt relay and an 18 to 20 volt zener.
