Guys: you might be right. It might need a battery, but it is so easy to test before buying new parts. After all a battery is >$100 and a starter even more. If after all of that you found it was actually bad connections or bad cables that would be a waste.
Confirm: When turning the key you hear a click but the engine does not turn over - or turns over very slowly and gives up before starting.
If it is the battery you should be able to start the car with a jump from another car or a jump pack. If you can jump start the car then I would test and possibly replace the battery. A quick battery test without running to the parts store for a load tester: Car not running and key off use your voltmeter and check across the battery terminals. At rest the battery should have >= 12.5V. If not you really have to charge the battery before testing with a load. This could mean you need a new battery, but there could be another reason the battery is not fully charged. After the battery has been charged: Key to start position measure voltage across the battery terminals. If the battery voltage drops below 11V I would condemn the battery. Hopefully during this test the starter is cranking the engine - even if it is cranking too slow to start. If your battery passes these tests and your car is still not starting you need to do some voltage drop testing to isolate the bad component. It could be the starter, but could also be cables or connections.