My girlfriend's Honda City's battery just died without warning.

Isn't the battery light supposed to light up to indicate a problem before it dies for good?

Not always, the battery have sufficient voltage when the engine is running but looses the voltage very quickly with stopped engine when the battery is worn out. The heat here in Thailand is very hard on car batteries.

When the battery started to die on my car, I could hear that it was hesitating (sometimes) turning the starter-motor and I knew the battery was shot and got a new one asap.

Battery light is only for charging system. Even than it's not always shows a faulty alternator. Older german and english cars have a volt meter, there you can read the condition of battery and charging system. Buy a digital volt meter for plug in the cigarette lighter. So you can see, if you turn your ignition on and the voltage is below 12 Volt, that something goes wrong. So soon as you start your car, the alternator should charge at least 12'8 Volt, even if you turn the headlights and the AC on. Some Bosch Systems charge 14 Volt, Japanese usually 12.8 to 13.5 Volt. The voltage of your Battery (when engine not runs) should be above 12 Volt.

100 % good battery should show 12.7 volts, engine off. Anything below this shows it is on the decline.

Battery light is only for charging system. Even than it's not always shows a faulty alternator. Older german and english cars have a volt meter, there you can read the condition of battery and charging system. Buy a digital volt meter for plug in the cigarette lighter. So you can see, if you turn your ignition on and the voltage is below 12 Volt, that something goes wrong. So soon as you start your car, the alternator should charge at least 12'8 Volt, even if you turn the headlights and the AC on. Some Bosch Systems charge 14 Volt, Japanese usually 12.8 to 13.5 Volt. The voltage of your Battery (when engine not runs) should be above 12 Volt.

Where can you buy one of these voltmeters which plug into the cigarette lighter? Is this a specialist thing or will any Big C or Tesco stock them?

Thx!!!

Where can you buy one of these voltmeters which plug into the cigarette lighter? Is this a specialist thing or will any Big C or Tesco stock them?

Thx!!!

Never seen them over here, but you could always buy a volt meter instead, comes in handy for many other things to check too.

Most electrical retailers sell them around 500bt.

I maybe wrong but I don't remember seeing a cigarette lighter on my wifes 1 year old city.

Buy a cheap volt meter. Be sure to set dial on the direct current 20V. Start the motor and it should read in the upper 13V area. Leave car over night, do not start it, test battery, if good condition it should read 12.7+, if below then it is on the decline, even 12.4 can mean it is near dead.