A battery warning light does NOT mean the battery is bad - it means your charging system is not charging. Drive much further and you will end up stranded with a dead battery. Here are the most likely causes ranked by how often they turn out to be the problem.
The most common cause. Worn brushes, bad diodes, or failed voltage regulator drop output below 13V. Tested with a meter in seconds.
The belt drives the alternator. Snapped or slipping = no charge. Visible in 30 seconds with the hood open.
Green or white crust on the terminals adds resistance. Clean with a wire brush and baking soda or replace badly corroded ends.
An old battery (4-6 years) cannot hold charge even with a working alternator. Test at any auto parts store free.
The engine-to-chassis ground strap can corrode or break, leaving the alternator unable to send full current.
The car loses power steering, AC, or the dash lights start dimming. The car is running on battery only and may die in minutes. Drive directly home or to a shop and dont turn it off.
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Short distance, yes - usually 15-45 minutes on a full battery. Turn off accessories. Get to a shop fast.
No - it means the charging system is failing to charge the battery. Usually the alternator, belt, or wiring, not the battery itself.
Alternator: $300-$800 installed. Belt: $100-$250. Battery: $150-$350. Ground strap: $50-$200.
Intermittent connection - loose belt, loose cable, or worn alternator brushes. Will become permanent soon.
Yes, if internal resistance is too high to accept charge. But the alternator is the more common cause.