Yearly dead battery

[Geoff35]

Hi I have just acquired my first jag, I have known the car for a few years now and it's previous owner has got rid due to what has proven to be a very annoying fault. Every winter the battery fails, it is fine all year then as soon as the weather gets cold the battery has to be replaced. This surely is not right, any ideas on where to start to stop it happening.

[Guest]

You are absolutely correct this should not be happening. What quality batteries have been fitted and what sort of guarantee did they have? Presumably the batteries had to be changed because they were defunct and not just low on charge. It is a simple test for a garage to check out the charging circuit of the car to ensure it is charging the battery correctly, so it may be worthwhile having this done. However if all is OK the quality of batteries being fitted has to be called into question, a decent battery for an S Type is £100 plus. I cannot see it being a fault on the car other than something amiss with the charging circuit and this would only result in a low battery and not a knackered one. Sorry I can't be of anymore help, hope you get things sorted. Best wishes Geoff.

[Geoff35]

The last battery was over £100 from Halfords, from experience not bad batteries, will get the alternator checked out. Frustrating!

[volor]

Just a quick thought but is the right amp battery being installed? To low an amp battery especially for crank load will work fine during the summer, but when you get to winter, all the oils (engine/gearbox) thicken up and the battery cannot spin the engine fast enough, and can lead to flooding. Seen a number of V6's fitted with smaller batteries than required, especially auto's and in some cases supplied like that from new by the manufacturer. I tend to check using an internet based battery supplier. Not for the 1st time have I bought a car fitted with the wrong rated battery from day one.

[Geoff35]

The battery is huge, looks like it would be good for a truck! Have checked and it is the right amp.

The previous owner only did very small journeys possibly 2 miles each way every day of the week, wondering if its possible that the extra winter heating, lights, heated screens etc have killed the battery off. The car probably not even fully warmed up by time it got parked every day.

[volor]

Well - short runs will certainly drain the battery over a period of time, especially with all the accesories being run :), but a good overnight trickle charge should return it to health, until it needs the next boost. The way I have read the post is that the battery actually dies and cannot hold charge..... If that is the case it could be something like the Voltage Regulator in the altenator may not be to clever and is overcharging and leading to overheating the battery, which will eventually kill it. I take it you have tried to trickle charge it, and it won't hold charge? Also am assuming it is a sealed unit.

[Geoff35]

I had not attempted a trickle charge when 1st posted this but did do a slow charge over sat and Sunday, and it seems to of held the charge up to now, although I have not driven it but it dies lock and unlock correctly now and the alarm light is flashing merrily, so looks promising, be interesting to see if it starts on Sat when I need to drive it.

[volor]

Hopefully that may have sorted it. I could go on about how some Batteries (under certain conditions) can get into a memory lock position re charging ... but it is long and boring..... but a trickle charge 9 times out of 10 will break the pattern.... so here's hoping. If it does work, go and enjoy a nice long run in your Jag, that should allow the battery to relearn it's correct charge level.

[EricG]

My dear old "S" Type, first registered 1/9/01 suffered badly from dead battery problems from the outset. Often used for short journeys, the problems were worst in the winter months and the battery would often be completely flat if I did not use the car for a couple of weeks for example. The first battery eventually failed completely when it was four and a half years old. The replacement battery is still going strong after nearly 7 years. I am convinced that this is because I took the advice of the AA back in 2006 and bought myself a trickle charger from Halfords. I have since that time made sure that the battery is never allowed to run down and it takes little effort to put it "on charge" about twice a month.

[pronea]

Hi Geoff,

Did you measure the current that is used when everything is switched off. I mean measure the current with the key not inserted and all doors closed, so no interior light is on? Just disconnect the ground connector from the battrey and place a Amp meter (a multimeter will do to) between the battery and the connector

If this current is too high it will drain your battery too.

Best regards,

Job.

[Geoff35]

No not tested that, exactly how do I test and what readings should I expect?

I get the disconnect battery earth part but which connectors do I put the multimeter between?. Sorry but electrics baffle me ever so slightly :-(

[mictop1961]

You place the ammeter leads between the earth post and the earth cable, there should be no reading an the ammeter with everything switched off. All this discussion of trickle chargers doesn't make sense, if the correct battery and the charging system is working correctly there should not be a problem with starting the car. The charging system should be charging at approx 14.5volts, have you checked this?

Another thing to check is the good old fashioned one is the boot light stuck on, or maybe a faulty alarm, just check the basics before rushing out to buy a charger because using a trickle charger will mask the real fault.

Perhaps another check is the starter motor this can be sluggish on a cold morning it could be this, that is the problem?

Few things to check hope they help

[volor]

Trickle charge will make perfect sense in a car that does not get regular use, and the discharge from the battery is greater than the charge from a short run. A car sitting in a garage will still discharge because for example, the alarm on, the clock is still running, and the engine ECU will be taking a current. That is a fact. Then chances are you start the car, the a/c is on, heated screen kicks in, etc..... and unless you do a decent run, the battery will never be recharged to the level it was before you cranked the engine (which is an enormous load, especially in an auto, as you cannot disengaged the gearbox by depressing a clutch, when u start). In most modern cars ( like last 20 yrs) if the amps are to low, the pre starter solenoid will not activate, and prevent the car from starting. Welcome to the joys of modern cars with advanced electrical systems.

[Guest]

mictop1961 is right, if the battery is not faulty and the charging system is OK there should be no need to use a trickle charge to keep the battery up to scratch even with an infrequently used car that only does a low mileage, if you do there is a problem somewhere. Good luck with it, Geoff.

[mictop1961]

Sorry I stick with what I said the car should be able to stand for at least a week without a trickle charge, heated rear screens ect don't come on until the engine/alternator is running and the clock will take a very small current to make any difference,The advance in modern electronics is that they only draw a small amount of current to run, I have yet to see any documents (I actually work in the bus industry) that state that you have to buy a trickle charger when you buy a new car!

A trickle charger is designed for cars that are stood for long periods not for a car left over two or three days without running.

Geoff I think it may be best to take up the services of a decent auto electrician, they can tell you what is happening with the charging system and if there is any large current draw on the battery when the car is at rest.Is the battery at fault as I stated before the starter motor could be at fault in the summer it has an easier job turning over but when it is colder weather there is alot more load, again an auto electricain should be able to check the current draw on the starter system.

Good Luck,

[Geoff35]

Thanks for all the advice, so far since I gave the battery a good charge it has been faultless, I only use the car at weekends as I use a works van during the week. And not one flat battery, leads me to think that it was literally all the very short runs not giving the charging system chance to work.

Hopefully this will be the end of my flat battery issues but will be sure to come back if I get issues

[volor]

Geoff,

Good to hear that a slow charge appears to have done the trick. Enjoy your Jag.