Charging systems and batteries

[History]

Dynamos and alternators on cars arent actually capable of recharging a battery.

The reason is that a std lead acid battery needs to be charged at 14.4 volts for 36 hours to charge to 100%. Which is 12.6 volts for six cells. This voltage is measured with battery disconnected. 12.3volts is 50% and 12v is 0%.

Any battery that is maintained at less than 12.5 volts will duffer early failure. This is why battery last less than 5 years.

When the car is started a bit is taken from the battery the generator then recharges but unless you drive for 36 hours then the battery never gets to 100%.

So once a month charge externally at 14.4 volts for 36hours. 14.4 is the max gassing occurs at 14.5 and higher. This external charging doubles battery life.

car generator are best set to 14.4 volts. This stops gassing.

Note figures quoted are for lead acid. Calcuim and agm and other types of lead acid batteries ( all have lead and acid somewhere) are a bit higher Ford are quoting 14.8 volts as gas off point for their silver batteries.

I am terrible at leaving lights on so I charge once a fortnight.

Regards
Bob Reddington.

[tractorman]

And the charging current has a lot to do with the speed at which a battery can be charged - hence an alternator on more modern vehicles. However, if memory serves, an alternator needs a certain level of input voltage to make it charge - a dynamo will do so without it.

As for longer term storage, I disconnect the earth lead if I don't intend to use the machine (tractors mainly) within the next fortnight and admit that I am remiss at "maintaining" them (ie I forget!). I charged the three batteries that haven't been used for nearly a year a fortnight ago and, because of a query on another forum, measured their voltages. The ten year old one was at 12.4v, the three year old at just over 12.5 and the unknown one (off the Land Rover) was nearer 12.6 - 12.5 something. It was last November when I last put the charger on them and, on both occasions, it reckoned they were fully charged! I haven't bothered to check with hydrometer or under load, but I am confident they will all start their engines without problem. The tractors both have dynamos and the Land Rover had an unknown model of a Magneto Marelli alternator. I parked the Land Rover up in Sept 2013 and forgot to take the earth lead off. I was most surprised when, on a freezing cold November day, I was able to start the beast!

[TerryG]

Not to disagree with you but I have cars at 10 years old still fitted with the battery they were supplied with new.
If every car in the country had to have it's battery removed and charged externally every month millions of motorists would be demanding the problem was fixed!

[JPB]

Modern batteries just don't seem to last as well as older ones did. I believe that the statement I just made there has one of three possible explanations:

1) Cars with dynamos rather than alternators were much kinder to the battery, albeit at the expense of efficiency.
2) I'm getting older so the length of time a battery lasts these days is the same, but its lifetime is a smaller percentage of the total number of years I've been around.
3) I'm getting older so am even more likely to leave something switched on all night which, combined with too many full discharge cycles, will reduce the life expectancy of a battery even if [the battery] was a fresh one within the last 10% of my life.

[TerryG]

Just because I'm a pedant I have been outside and checked, Mog's battery is dated January 1998, 2000 focus has a sticker on it's battery saying "next check due 07/2002" As I have had it since before then and have never replaced the battery that is doing well. It has been run flat a few times as the cigarette lighter socket for some reason is always live so if you leave your car charger in and go on holiday for 2 weeks, it is dead when you return. My '05 had a new battery 2 years ago attempting to cure a starting problem that turned out to be the cable between the battery and starter solenoid. It's original battery is fine (and huge), sits on the floor in the garage just in case something needs a jump.
Batteries are something I fit and forget. They don't need maintenance or attention as they are all sealed. The day the car struggles to start it's time for a new one. Life is too short to lug them in to the garage once a month for a charge.

[zipgun]

Noo , when we were young tearaways ,out every evening ,we used lots of rpms and that made lots of juice !!!! .
My Suzuki Swift battery died (swiftly.. ) on its third birthday, my T4 original Bosch battery died after 11 years , its Bosch replacement is dying at 3 years..
The 1.9td engine does ,as always has , started instantly, first kick ..so no great load on the battery .

[History]

The information I posted is correct and comes from experts such as the AA and RAC.
Batteries that are never charged by externals means will fail early say 5 years. The average new car buyer changes the car before 5 years so the early failure goes un noticed. The new owner gets battery failure say 1 year after purchase, but its a secondhand car so its par for the course.

It is not possible to fully charge any lead acid battery fast. The extra amps just gas off. The electrons have to travel deep into the battery to deep charge. It takes 36 hours and that's that.

Most of you will have battery chargers so there's no harm in a long deep 14.4v charge up.

Note 36 hours can be split up to three lots of 12 hours. I dont leave chargers on over night. Fire hazard.

Bob Reddington.

[tractorman]

I can't argue about modern lead-acid batteries as the tractor batteries get the odd day on charge through the year as they don't get the use to keep them fully charged. However, the first two VWs (85 Golf and 98 Passat) lead-acid batteries lasted at least seven years, though the alarm went faulty on the Passat not long after the first battery was changed and would drain the battery over a weekend! The Mk4 Golf's battery lasted about seven years too, but it was a calcium thing. The current Mk5 Gold (late 2008) is also on its original battery (again, a calcium thing!), so I'm waiting for that to pack up! Mother's Metro (1988) only had one replacement in the seventeen years she had the car - and it never saw a charger until just before the original one failed. As it happened, the battery on the Fergy was the same size and was used until we got a new one for the Metro. The Fergy battery must have been more than ten when it eventually failed - I had the tractor for over ten years and it was an old battery when I bought the tractor! However, it often need a session on the charger!

There is a problem with statistics - they include the bad things - like the three batteries the first Golf used in the four years after the original one failed, the Maxi that would eat batteries, my friend's Transits seem to get through them very quickly (his 2012 one is on its second one) and my friend's tractors that seemed to need new batteries every three or four years.

There is one thing though - how "dead" are the flat batteries? Fair enough, a new and uncharged battery will take time (overcharging can buckle the plates), but how often to normal batteries get to that level? There's a big difference between not turning a starter motor quickly enough to being so low it can't light up a 2W bulb (or a 2W 1.5v one!). Remember - we are talking "practical classics" not "theoretical scenarios" and most of us won't ever see a totally dead battery. OK, we will see ones with "blown" cells, but not one that is totally flat that could be restored by "deep charging".

[JPB]

experts such as the AA and RAC.

Ex = has been. Spurt = a small drip under pressure. Some of their people know their stuff, many come to these organisations from a different industry and take a course that lasts a few weeks after which they're expected to know... What exactly? The phone number of their closest recovery unit is what! Gone are the days when they could actually mend anything by the side of the road. OK, so they can if the repair can be made at the nearside but they have to move the car if the repair would require their working at the offside, just in case they get squished by a truck which I understand, but come on, surely these so-called "exspurts" are quick enough to get in about at it and be done before the truck appears.
Back in the eighties, etc..

[TerryG]

A batteries life may be reduced by not removing it from your car and charging it fully after every run but I know that as the batteries in my cars are all older than you statement is not accurate.