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Extending car battery life - Is it possible ???

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As a newcomer to the world of electronics I need some help. My other hobby is old cars and I am forever buying new batteries as the old ones fail regularly due to long periods of inactivity followed by heavy discharges and rapid recharging. The problem would seem to be the excessive build up of sulphates on the lead plates reducing the ability of the battery to take and retain a charge. I have read that using square wave technology this build up of sulphates can be prevented and even reversed. IS THIS TRUE ? Can anyone explain how this works and help me with the design of a device I can use either occasionally or even leave permanently connected 'on the car'.
Any suggestions or advice would be greatly appreciated.

Hi Steve,

I also have a couple of old motors that i keep and start up every
so often. I have found exactly the same problem. The official line
is to keep the battery well charged to maximise its life. I have
never found this to work. I have given a lot of thought to this
very problem and i am in the process of implementing a possible

My (possible) solution will be to charge the battery to as high a
state of charge that it will accept, and then to empty out its
fluid and keep that separately in a glass jar with a lid or seal
that can cope with sulphuric. The battery i will allow to dry out.

When the battery is required, the battery fluid can be replaced.

I have to say that i have not tried this procedure yet, and i do
realise that due care will be required for personal safety and to
avoid spillages which can cause no end of trouble, as i know from

If in fact this works as i hope it will, then my batteries will
hopefully last for many more years than they have been up to now!

If you have any thoughts on this,
or other suggestions to prolong battery life,
i would very much like to know.

Regards, John :)
A battery will last a long time if it is kept fully charged. The charger should start charging at 12.6 volts and stop at 13.8 volts, altho those numbers vary with temperature. If the vehicle is in a location where the temperature is very high or very low at times, temperature compensation is required. I doubt very much that waveform is important, the unfiltered rectified current should be fine. A constant current charging source that does not cut off as the battery voltage rises above 13.8V will deplete the liquid, allowing the plates to dry out, which reduces life.
Hi Steve,

About the square wave business,
No i don't believe it makes any difference.

The only way i know of to deal with the sulphate build up is to take
the battery apart and physically clean the plates.

Also i don't think that its just sulphate build up, i think that the
'dosing' or 'doping' of the plates to give them a preference for
negative or positive, is also affected and deteriorates, why i don't

Cleaning plates these days has to be done carefully, they are no
longer made of sheet lead, it is now a form of pressed granules like
a biscuit, this gives a greater surface area, and improves maximum
discharge current, but also makes them physically weaker so that the
separators are now also part of what keeps everything in place.
Cleaning the battery plates is a last resort when all else has failed.
Most batteries are not made in a way that they can be easily taken
apart and put back together. If i do this i generally do it with the
battery upside down, after separating the casing, usually by physical
damage to the fixing around the top. I would rather do small damage
to the top than to the casing, as i have never found a satisfactory
glue to use for repair to a damaged case, but around the top, pitch
will usually be ok.

Best of luck, and please keep me informed as to your progress,
Regards, John :)
I found a great site (can't recall the URL) by a company with a keen interest in getting long life out of lead-acid batteries. I was left with the impression that there is much that can be done

I've just seen the post from Russlk,
and i agree, allowing the battery fluid to dry out by
evaporation is known to be bad for batteries.

I am hoping that when i empty the fluid out, this
will not cause a problem.

It is possible that the evaporation of the fluid leaves
behind a layer of whatever may have been in solution
or suspended within the fluid, and causes problems.

I am hoping that emptying out the fluid after charging
and allowing the battery to completely dry out,
will not cause the problems that occur from allowing
it to evaporate.

However, i don't know yet. I haven't tried it yet.
When the warmer weather comes around, i will be trying
this out.

Cheers, John :)
Hi stevez,

if you find that site again,
please post it !

John :)
Some interesting ideas are being tossed about here. Regarding draining the battery fluid, I very much doubt that would be a good idea. The plates will still be wet when the fluid is drained and they would sulfate as they dry out - my theory, you prove me wrong :wink: .
They do ship new batteries minus the acid but these batteries never had acid in them in the first place.
Those of you who take the top of a battery off in order to clean the plates are a lot braver than I. Acid is dangerous and I wonder if the little battery live gained is worth the very large risk of getting acid burns ?

Regarding battery rejuvenation of sulphated plates, there is a circuit on the net of a "battery desulphator". Do an advanced google search, the drawing I have says 'Loring Engineering Services Desulphator - 12V- Enhanced Turn - off' but does not show the URL.
I built that device to resurrect old deep cycle batteries. It does appear to work but there are no instant brilliant results. An old battery is an old battery :) . I got some more useful charge out of the battery but it did not revert to the capacity it had when new.
This desulphator is more useful for deep cycle batteries, the thin grid plates of automotive starter batteries are usually too far gone after a few years of service.

So, to your question " extend the life of a car battery" my answer would be that after a few years of service (REGULAR use - charging and discharging cycles) it's time to renew it - they are designed to wear out. Their shelf life is not indefinitely either, check the date stamp code when you buy a new battery.

Had you asked how to shorten the life of a car battery I would have mentioned to leave on the headlights on regularly when you park, to never check the acid level (if its not a sealed battery), to have a poorly functioning alternator and to use the car only once a month :D .

For older cars that are used only for special occasions you could perhaps use a battery exerciser, a timer that connects a load across it for a time every day and a regulated charger that keeps it topped up in between. The usual battery service still must be done.
Of course, the engine ought to be turned over regularly too to keep things oiled so why not start her up and run until warmed up at least once a week and exercise the battery with that at the same time?
Hi Guys,
Interesting topic.

From my experience the only way to make an automobile battery last as long as possible is to exercise it and never let it run dry. It thrives on heavy discharge at starting time and quick recharge. They should be charged up (not necessarily in the vehicle) at least once a month.

To get rid of the sulphation you need to give the battery an equalising charge by raising the charging voltage to 2.5 volts per cell for about 8 hours depending on how badly sulphated the plates are. This will cause the sulphate to come away from the plates and drop to the bottom of the battery. Under normal operation the sulphate builds up at the bottom and eventually shorts out the plates causing cell failures. It is not sensible therefore to turn the battery upside down to empty the electrolyte. The
sediment will find its way between the plates and cause trouble. Manufacturers can make car batteries last longer by leaving a deeper space between the bottom of the plates and the bottom of the battery case.

You could tell them that I said so!

i saw this posted on another forum... basically it just keeps the battery charged, maybe it'll help in some way? not sure what to think of it or how to implement it, and all that there is is this schematic... nothing more. maybe other users on here can give there own intrepretations of it.


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John - I'll try to find that site. I think Trini's comments are in line from what I recall. My initial comment was hurried - phone call. I also drew from what I learned, that for a low cost battery the relative cost of the equipment to extend the life might be high enough that it would make more sense to accept the shorter life and replace the battery. Not all batteries are inexpensive. Here in the US I can purchase a battery that is sufficient for my vehicles for about $40 - sometimes less.
Long life for your battery

The way to mantain a battery completely charged, after a correct recharging cycle, is fundamental. If you permit that part of the plates remain discharged, they will build up a kind of sulphate that is very difficult (sometimes impossible) to get back to the original form, lossing gradually capacity.
The complete cycle takes the initial charge (about 90 %), the equalization or overcharge, and the floating state. Each of this stages must be controlled for voltage, current and temperature correction.
The simple way to get a perfect sequence is to use a simple IC:
UC3906, it does everything perfect. See the specs and the application note at
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