car battery

aucklander: Hi all,

last week-end I got the car out for a wash, and 2hrs later it did not start anymore. Well, I said to myself, this is what batteries do... they just die with no warning. Bad luck. When I checked the water in the battery, some was missing and to my surprise, I needed 1L to bring the level where it was supposed to be (I used demineralized water). There were no leaks from the battery, something else might have happened. Doesn't matter anymore. I started the car using the other car, let it run for 30min, then everything was good. It then started OK every morning to go to work and every evening to come back home (approx. 30min drive each way).

Next week-end (yesterday) the car was not used at all and Monday morning did not start anymore. Water level was OK. I needed one of those AA rescue vans to come at home and start my car so I can (finally) go to work. They also run a diagnostic and the recommendation was to have the battery charged by an auto shop on one of their large capacity battery chargers.

Here is the point of this post: I was under the impression that the car's charging system is more than capable to charge the battery without any help from outside, but the AA technician told me that this is OK for "normal use". In this instance the battery went completely flat, and the charging system CANNOT re-charge the battery from that state and this is why the need for a larger charger. The car's charging system can re-charge the battery to compensate for normal use (start-ups, listening to radio in the car park for 2 hrs, stuff like that) but if the battery goes flat then you can start it with another battery, but it needs to be charged on a separate (larger) charger in order to regain its full charge.

I do not want to question what the AA guy advised, but... does this makes sense?

The car is now with an auto shop close to where I work and when I go there to collect it at 5 p.m. they will also do a "load test" to assess how well the battery performs. Only after that I can make a decision if I need a new battery or not. Is this how it goes? I was under the belief that once the battery stops retaining the charge, you need a new one...

Depends on how long the engine will be running for after you jump start it. To be safe you would want at least 1 hour of engine running to fully recharge the battery. (or to at least bring it up to 80% or so) And that is with headlights, aircon and other big power users switched off. The other risk is if you completely drain down a newish battery and then jump start and drive the car You might burn out your alternator. This is because a discharged but still good condition battery can soak up alot of current when being recharged. If you get your car jump started best is to leave the engine idling for 1/2 an hour or so first. With unnecessary loads switched off of course. As the low engine speed will limit the alternator output. And if you have to drive immediately try to keep engine speed low.

The other issue is some modern cars use active management of the alternator output voltage as a means of improving fuel economy. On these cars you will definitely need to recharge the battery fully first. And same on those cars that automaticly stop and restart the engine to save fuel.

So my guess is that some at least of what the AA guy said was butt covering.

aucklander

Aredwood