Install an ammeter in the battery positive lead - start the engine and turn all the accessories - increase engine rpm until the meter is reading ZERO amps - the RPM of the engine at that point is the break even point (the charging system is supplying all the current drawn by the electrical equipment) - at the break even point, the battery is neither being charged or discharged. Now raise the engine RPM until the ammeter is indicating 1 amp - this is the speed the engine needs to be operated at for 5 to 10 hours to fully charge the battery. Any time the engine speed is below the break even RPM, the battery is discharging - if the engine is operated at below break even RPM for longer periods of time than above the break even RPM, the battery is dying while the vehicle is in operation.