Alternator failure and battery failure produce similar symptoms — the car won't start, electrical systems are weak, dashboard warning lights are on. But they're different problems with different fixes.
Battery failure: vehicle won't start cold, jump-starting works but the engine dies when the cables are removed (because the alternator can't power the vehicle alone — too much load).
Alternator failure: vehicle starts and runs initially after jump-start, then dies after a few minutes as the battery (which is now powering the entire vehicle) drains. Battery warning light on dashboard often illuminated. Headlights dim during driving.
The test: jump-start the vehicle and immediately disconnect the cables. If the engine dies within seconds, the alternator isn't working. If it keeps running for minutes, the battery is the problem.
Alternator replacement runs $400–$900 at a shop. Battery replacement runs $150–$300. The repair cost gap is significant; correctly diagnosing the problem first saves money.