A battery that keeps dying is almost never a bad battery. Twice.

What it usually proves to be (in order)

1. 1Parasitic draw — something staying awake (a trunk light, an amp, a module that will not sleep)
2. 2A charging system fault: alternator output, belt, or wiring — testable with a meter
3. 3A corroded or loose ground strap masquerading as a bad battery
4. 4Weak-battery phantom fault codes that make modules look dead (U-codes)

What a parts-changer will tell you

Sell another battery ($200–$350), maybe an alternator ($800+), and a computer when U-codes show up. The draw or ground fault is never measured, so the problem — and the battery — comes back.

Typical guess-and-swap cost: $200–$1,200 (battery + alternator) when the fault is a $12 switch or a $40 ground strap

The test that proves it

Battery/charging load test, then a milliamp parasitic-draw measurement with everything asleep, pulling fuses methodically. The real Glass Box case: a 340 mA draw traced to a trunk-light switch that stayed closed.