How do you know when a battery is dead and needs to be replaced?

My car is about 5 yrs old, and the battery did run out once when I left the car sitting there for 3 weeks. Seemed odd that a battery would run out in just 3 weeks of no driving. So thought the battery is almost dead ...

Then started reading all these threads here, and seems like a weak start on the engine is an indication, or if the battery dies within days since the last drive. I don't seem to have either of the issues ...

So am wondering whether I should bother with changing the battery at this point ... any thoughts? Thanks

 

Test it with a battery tester

 

Load test a garage. Most garages in NA would be able to do it, I assume HK would be the same!

 

My battery was "fine" during the summer, but when it got cold it started to complain. So I replaced it early rather than be stuck somewhere without power. A battery is the cost and hassle of a taxi ride from some places.

 

except a battery in Hong Kong costs nearly 900 USD

Can get cheapo ones for around 100 USD. Not sure why the original OEM one is 900 USD, it's a bit absurd ...

 

No need to get OEM.. In fact, I don't even think we can get OEM Panasonic bats from the dealer here in the US. Cheapo 'name brand' batteries should work just fine..

 

Very helpful to use a digital voltmeter, which plugs into the 12V accessory socket. At rest, the voltage should be at least 12.0. Turn on the lights and blower without starting the engine, and it should drop no more than a few tenths of a volt. Drop should not be too severe when you hit the starter. You can also check the voltage while the engine is running - should be around 14 volts. I had one dead battery which would put out that 14 volts, but periodically, for a few seconds every minute or two, would drop down to 12. The problem was evidently an internal short between plates.

 

when i was fixing my top i had it up and down a few times with the engine off, do that, if your car still stars right up, cranks fine then you don't need a battery yet. mine lasted from 10/03 till last month.

 

Mine lasted from Dec 99 to Dec 08

 

In my experience you will notice a day or so before it goes it takes a bit to start the car up, plus the cluster will dim with each turn of the engine.