What does "1/2 charge" mean? If you mean a dash voltmeter shows a drop from 12 V to 6 V, you need to locate the drop. Most commonly it is from corrosion right at the battery terminals (why even mini-marts sell battery brushes). Removing, brushing, and spraying with anti-corrosion should be an annual task on all vehicles in TN (bi-annual out West).
Crank while you monitor the voltage difference between BATT- and BATT+ lead posts (not the connectors). If that remains >12 V, then don't fault the battery. Similarly, if your starter doesn't get >8 V from input big stud to its case, don't blame the starter.
