Published 23 Jul 2026 · 4 min read
Car won't start but the lights still work: battery or alternator? A 5-minute check
Short answer first. If you turn the key and get rapid clicking or slow, laboured cranking while the headlights and dashboard still light up, the most common culprit is a weak or dead battery.
But if the battery warning light comes on while you are driving normally, that points at the charging system, the alternator. You can separate the two before reaching for any tools.
Symptoms that point to the battery
- Rapid clicking with no cranking, while the interior lights still work
- Starting gets gradually harder, with slower cranking, especially in the morning
- Headlights dim noticeably with the engine off, or while cranking
- The car sat for days and would not start, then ran normally once jumped
- The battery is past two years old, which in Thailand's heat is its final stretch
Symptoms that point to the alternator
- The battery warning light comes on while driving, which signals the charging system rather than the battery
- The car dies again soon after a jump, because the alternator is not feeding charge back
- Lights pulse with engine revs, or several electrical systems act up at once
- A recently replaced battery keeps going flat, which points at the charging system
The jump start and voltage test
A jump start is the best no-tools test there is. If the car starts and keeps running, the problem is mostly the battery. If it starts and then dies again soon after, suspect the alternator.
With a voltmeter, a healthy battery reads around 12.6 volts with the engine off, and should rise to roughly 13 to 14.5 volts once the engine is running. If the reading does not rise at all, the alternator is not charging.
No meter is no obstacle. Any battery shop, ours included, can test both the battery and the charging system in minutes.
Why the battery usually goes first
Heat accelerates battery wear, which is why batteries here average only around 2 to 3 years, clearly shorter than in cooler countries. Alternators, by contrast, tend to last much longer.
So if the battery is past two years old and the symptoms match the battery column, start the diagnosis there and work toward the charging system only if they persist. If it does turn out to be the battery, our guide to choosing a cheap car battery without getting burned is worth reading before you buy.
If it is the battery
Do not risk driving a car that barely starts to a shop. Use our mobile battery replacement service in Korat: tell us the make, model, year, and where the car is, and we confirm the right battery and the total price by phone before any work.
The technician comes to you and fits it, with a basic electrical check included. If the on-site check suggests the alternator rather than the battery, we will say so, and the shop stocks alternator parts too.