Jump starters

Rover_Driver

bigjl wrote: »

The alternator failed on the A4 and completely discharged the battery.

The discharged battery was not charged by Jaguar, probably because the Tech involved was of the same opinion as you, in this case the wrong one.


The same car a few days after getting it back would not allow me to sit listening to the radio for longer than 5/6 minutes before setting of the low battery warning.

It improved back to near previous levels after a proper overnight charge.


Here is a link that might prove helpful.

https://www.optimabatteries.com/en-us/experience/power-source/fact-alternators-are-not-designed-to-charge-dead-batteries/

As in that link, an alternator will not, and is not designed to, charge a flat battery.

What you described is the typical problem between fast and slow charging of a lead/acid battery.

The alternator regulator will control the output to the current demand, if the battery is low the current flow will be high, which is not good for the chemical reaction within the battery and can result in an insufficient charge.

A slow, longer, 'trickle' charge from a mains charger is better for the chemical reaction within the battery and can result in it being charged to its full capacity. Then when kept charged by the alternator, it will maintain that level of charge.

arcon5

Well i'll be damned, we've been getting it wrong all this time. If we have to jump a car on the car lot we've been leaving it running to charge it up if the battery charger is in use.... I guess the batteries was in fact charged by fairy dust and not by the vehicles charging system

Rubidium

Iceweasel wrote: »

Fortyfoot - while I appreciate you are asking about a jump-starter, that will certainly fix your problem - but only in the very short term, by getting the engine running, rather than doing anything about the underlying problem.

Taking more out of a battery than you are putting back in after starting is quite easy - especially in winter, with cold starts, lights and heaters etc.

Couple that perhaps with short journeys and the battery has no chance of being replenished,

I'd give serious thought to getting a 'Smart-Charger' as others have suggested, and keep your batteries fully topped up.

Prevention is better than cure.

A Smart Charger is also considerably cheaper than a booster starter-pack.

Lidl & Aldi regularly have them on special offer - mine cost £13.99

I completely agree.and I have been regularly using a smart charger bought from Lidl about 10 years ago.

Another thread derailed by irrelevant wibble about an alternators capability etc!

Rover_Driver

arcon5 wrote: »

Well i'll be damned, we've been getting it wrong all this time. If we have to jump a car on the car lot we've been leaving it running to charge it up if the battery charger is in use

As long as there is some power in the battery, an alternator will charge it, but not a flat battery - it needs a voltage supply to work.