Abstract: A vehicular battery charging system particularly adapted for railroad cars such as cabooses, in which an axle drive/hydraulic pump unit is coupled to the end of an axle via a flexible coupling and right angle gear drive. The hydraulic pump provides hydraulic pressure to a hydraulic motor/alternator unit. The a.c. output from the alternator is rectified and the resulting d.c. is employed to charge the batteries at a voltage which is very accurately controlled by a voltage regulator. The regulator comprises a switching circuit controlling the excitation of the field or rotor winding of the alternator by the rectified alternator output, in response to a repetitive pulse signal from a free-running multi-vibrator.