Alternator

[Geoff Peters]

Hi....having the battery coming on and off at various times....garage says it seems that there are times when the charge voltage is too low.  Battery is fine, no problem with starting etc. Any other ideas would be appreciated before having to buy new alternator...2'7 Diesel. 2005 s Type...Thanks.

[N6 JMX]

Hi Geoff, the ability of the battery to start the engine is not a good indicator of the battery condition these days. Even a 2005 car has a lot of electronics incorporated and these are very voltage sensitive. So, even though the car can be started by the existing battery, I would suggest that you get it properly checked by an Auto Electrician - if you don't have the tools and knowledge to do it yourself. Incidentally, perceived wisdom is to consider a car battery, lead acid variety, a consumable item and change when it gets to around 5-years old. Do you know the age of your battery?

A series of voltage checks will be required at various stages of the operation to truly assess the battery condition. I am sure someone will be along shortly to advise exactly what the various readings should be, but as a starter:

1. With the engine running, i.e. charging from the alternator, the voltage should be in the region of 14.6V

2. After a long run and stopping the engine, the voltage should be in the region of 13.6V if checked immediately on stopping the engine

3. If placed on a charger / conditioner, then fully charged should give a reading of around 12.8V with the reading taken at least 3 - 4 hours after disconnecting the charger, i.e. given the chance to settle

4. If the reading 3 - 4 hours after disconnecting from the charger were to be 12.5V, then the battery is potentially only at 50% charge

Please note that batteries are individual, subject to varying duty cycles and at this time of the year, winter and cold, they will not be at their best condition in any event.

N6 JMX