for given battery, your charger will be 13.8v, 7.5A
you can build charger by two methods:
1-switching mode power supply (hardest and complicated)
2-iron transformer (simple and less problems)
for charging stopping you can use simple comparator (ex.741) with small relay to cut off main power
for indicating voltage of battery you can use any dc voltmeter or any chip provide a logic output that shows a dc voltage on battery (ex.lm3914 drives leds) which gives you an acceptable feedback about battery voltage.
regards.