MX5 batteries flattening

Archives of Posts to the NZ MX5 List back in 2005
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joanie
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MX5 batteries flattening

Post by joanie » Sat Jan 22, 2005 5:59 pm

Greetings all,

We too have the problem of the MX-5 flattening its battery while car not
being used for some time, whereas our other cars don't seem to do this over
similar storage-durations. At least I THINK we've got this problem, although
for a definitive statement we need to actually note how long the different
cars sit unused in each case, rather than just guessing that the durations
are similar. Anyway, pending that exercise, I've made some current
measurements to see if the MX5 drew more on standby than our other cars, and
here's what I found -

Car 1, Alfasud Sprint, 8 mA on standby (analogue clock).
Car 2, Alfasud ti, 23 mA on standby (digital clock, display off).
Car 3, MX5, 20 mA on standby, with the alarm either set or not.

This shows me that the MX5 draws no more than the average 1980s
pre-electronic car, and so I can't see why our MX5 appears to flatten a
battery more rapidly than the same battery in an unused Alfasud. And I
don't see the 20mA of the MX5 as an excessive drain for a battery in a
unused car, so it's all a mystery. Nonetheless, it does seem to happen.

Any comments on these figures, anyone?
Best regards,
Graham Hilder,
Paekakariki.
1991 MX5

Colin wrote:
Properly installed, the immobiliser/alarm will not flatten the
battery prematurely. I have some equipment and ideas to make those
problems go away also.<

Mike Jolley

MX5 batteries flattening

Post by Mike Jolley » Sat Jan 22, 2005 7:02 pm

IS YOUR BATTERY DRY OR WET TYPE?
OURS FLATEND OVER 3 WEEKS OF NO USE,NEW BATTERY AND HAS GONE 5WEEKS
WHILEAWAY AND BEEN OK, MIKE

Grant
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MX5 batteries flattening

Post by Grant » Sat Jan 22, 2005 10:08 pm

What age is the battery? Rechargeable batteries of any type will self
discharge to some degree. As they age, this self discharge gets worse. An
old battery can self discharge to the stage where it won't start the engine
over only two or three days. It might be able to run the radio, alarm and
maybe even the lights, but due to increasing internal resistance with age,
it could have difficulty starting the car.
Batteries designed for starting service will self discharge at a greater
rate than those designed for standby power use. I don't know about the
characteristics of the genuine Panasonic original, but it does seem to last
a very long time before finally failing.

Grant.
Red 2006 NC Tiptronic
FIX A PC

joanie
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MX5 batteries flattening

Post by joanie » Sat Jan 29, 2005 12:34 pm

Hullo again all,

A week or two ago I posted some standby current-drain readings I'd taken on
our MX5 and two other cars. These showed that the MX5 drain (20mA) was not
particularly high compared with other cars, and also probably wasn't enough
to cause any abnormal battery-flattening while unused.

A reply from Mike asked about the type of battery (it's wet-cell), and the
age (there've been various batteries in it - they get swapped between cars
from time to time). And Grant also asked about the battery's age, noting
that as they age, their self discharge gets worse.

In reply, I'd note that yes, we're aware of this, and do take it into
account. But the question I'm really trying to home in on is, does the MX5
really have any greater battery-flattening problem than other typical cars?
The thing is, when we first bought our MX5 and started reading web sites and
mailing lists about them, this topic seemed to arise a lot. Everyone seemed
to be talking about their MX5 batts flattening while the car was out of use.
But now, I wonder if the MX5 is any different from any other car, in this
regard. My standby current measurements suggest not. So maybe the trouble is
simply that MX5s, being open sports cars, tend to sit unused for long
periods more commonly than do ordinary cars, and hence their batteries have
more opportunity to self-discharge in the normal way of a battery. I don't
know! So, what is the general view - has the MX5 genuinely got any greater
battery-flattening problem than other typical cars, or is it just a
perception?

Cheers all,
Graham H
One MX5, misc Alfas.

Colin
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MX5 batteries flattening

Post by Colin » Sat Jan 29, 2005 7:54 pm

Hi,

Mx5's don't drain current any faster than any other car of similar
electrical design. And there are millions of those.
The 'dry cell' or fibreglass mat/sulphuric gel battery supplied with
new mx5's does behave alittle differently than a 'wet cell' lead acid
type. This has caused some misunderstanding in the past and some
people have replaced possibly good batteries because of their symptoms.
If you are experiencing a high at rest drain then maybe poking around
in the relay box or simply unplugging things until the drain stops
will help identify what it could be. This is pretty much what your
Auto Elec will do.
If the drain is aok and the battery is a wet cell then checking how
fast the voltage drops across the battery when standing will help.
Mostly, batteries aren't what they used to be. Most of us still expect
to get many years from them. The truth is they often have only a one
year warranty. Any more than that could be a bonus.

I have a battery saver that allows me to plug the car into the mains.
It supplies a very small trickle charge that keeps the battery topped.
Hope some of that helps

Colin
Colin
021 869 231

Michael & Kate Cooper

MX5 batteries flattening

Post by Michael & Kate Cooper » Sat Jan 29, 2005 9:54 pm

The main problems regarding flat batteries that arise seem to stem from the
fact that the gel-type battery is a bit misunderstood.

If the gel-battery needs charging, a normal battery charger that you would
use on a wet-cell battery doesn't do the trick. It needs to be charged on a
trickle charger (less than 1.5A?). Many people have found that once they
have employed this method of slow charging, the battery that they thought
was stuffed comes up fine again.

I think that one of the oldies on the list wrote a really good description
of the physics and chemistry behind the gel-type battery a couple of years
back. Not sure if the archive search is working on the website yet, but if
you're into that kind of stuff it'd be an interesting read. (Went into
details of different chemicals used and electron-storage and stuff like
that, I think).

Our car had it's first battery replacement when it was 13 years old. We
bought another gel-type battery. Better statistics than our "other car."
(Which had normal wet-cell battery.)

Ciao

Kate

joanie
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MX5 batteries flattening

Post by joanie » Sun Jan 30, 2005 10:40 pm

Thank you for the respective replies, Colin & Kate. These are most helpful,
as from them, a picture of the situation is now emerging to me, such that
there may be two different issues being talked about in battery-flattening
discussions.
The first issue is that of MX5 batteries going flat while car sits unused.
The second is one of such batteries not recovering when recharged, and hence
being discarded at young ages.
From this, I can clarify that the second issue isn't what I'm trying to dig
into, as that issue doesn't arise with us - if the MX5 batt has flattened
while car unused, then we just charge it up and everything's tickety-boo,
exactly as we've done with our other cars that have sat around unused from
time to time.

It's the first issue above that I'm trying to clarify - i.e. do unused MX5s
flatten their batts more than other unused cars do?
On this, it's been agreed that our MX5's standby current, abt 20mA, is no
greater than that of many other cars, and in any case I don't think 20mA is
a big deal in terms of the flattening issue. So the level of standby
current can be disregarded as a significant factor. And since we use
ordinary batteries in our MX5 (batteries get swapped around amongst our
assorted cars as required from time to time) then the special battery-type
originally fitted to the MX5 can't be a factor either, in our case.

The logical conclusion has to be that (in our case, anyway), the MX5 can't
really be flattening its battery any more than the same battery left in any
other of the unused cars around the place. Any perception we've had that it
does do that would seem to be just our imagination (albeit, imagination
fuelled by the discussions we've read on the 'net!). But the only way to be
sure would be for us to make proper notes on how long the respective cars
sit around unused on each occasion and how their batteries cope with the
non-use. However it's not such a big issue for us now, as these days we've
cut down on the number of batteries we have in the place - we've got a good
few cars but only the MX5 and a couple of others are continuously
registered, so nowadays we only have three batteries. If another car is to
be registered and used for a while, we borrow one of those batts for it.

So these days the MX5, being a sunny-days sports car, is the only one that
sits around unused with a battery in it, and hence the only one we have to
keep an eye on. I know that letting an unused battery self-discharge, and
leaving it like that, will damage it, so from now I plan to recharge the MX5
batt periodically while car is unused. Since it's an ordinary wet batt the
standard simple charger we've always used on all our other batts will be OK.

Although it may be "OK", I'm aware that such a charger won't be IDEAL for
maintaining a battery in storage. The requirements for the long-term
storage-charging of battery are different from those of the simple one-off
recharge, and ideally you need a charger designed for the storage-charge
application (and also tailored for the particular type of battery you are
storing). I've done a bit of Internet research on this and I gather what's
needed is a constant-voltage charger, regulated to a voltage a little below
the gassing-point of the battery concerned. This is a simple thing to make
and it's on my project-list (but so are a hundred other things).

Regards,
Graham H

Mike Jolley

MX5 batteries flattening

Post by Mike Jolley » Mon Jan 31, 2005 8:05 am

Then you could start your mx5 for 2 mins each 2 weeks ,probably less hassle.
mike

joanie
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MX5 batteries flattening

Post by joanie » Mon Jan 31, 2005 9:23 pm

Might be less effort but would be very bad for the car and the battery! One
of the worst things you can do to a car is to repeatedly start it from cold
and turn it
off again before it's fully warmed up and had a good run. And as for the
battery, as I understand it, typical lead-acid car batts don't particularly
like being significantly discharged (as by starting a cold engine, for
example), and if in storage would much prefer to be kept charged rather than
cycled between discharge & charge. I really think an external charger is a
much better solution for battery-life.
Regards,
Graham

joanie
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MX5 batteries flattening

Post by joanie » Mon Jan 31, 2005 9:39 pm

Lyndon wrote -
You can really only disregard quiescent current draw from a battery after
you have measured it and know what it is.
To assume it is the same for all MX5s could be a mistake
and it only takes a couple of minutes to check it.<
On this, I have measured ours as mentioned, and while it's true that only on
our car do I know the drain is 20mA, our one's a very typical early MX5 and
if another example had significantly greater quiescent drain then you'd have
to ask if there were a fault in that case, I think.
The other issue is battery condition...
As we all know, normal car batteries that sit around unused for weeks at a
time will self discharge.
When the voltage drops below a certain level they begin to sulphate.
These sulphides form on the plates and begin to deteriorate the performance
of the battery.

Yep, agreed. This applies to every battery in every unused car of every
type. The question is, though, why does it seem to be a
particularly-discussed issue in the case of MX5s?
The way to [avoid sulphation] is to keep the batt voltage above the level
at which it begins to
form.
You can buy small Charge and Maintain trickle chargers from Kmart, Repco etc
and in theory these should do the job???
Yep, they should, provided they are properly-regulated constant-voltage
chargers, and are regulated to the appropriate voltage for the type of batt
you're maintaining.

Cheers,
Graham H

Mike Jolley

MX5 batteries flattening

Post by Mike Jolley » Tue Feb 01, 2005 6:57 pm

put all your energy worrying about the battert into i and you could charge a
fleet of mx5 owners)
tounge in cheek answer

joanie
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MX5 batteries flattening

Post by joanie » Fri Feb 04, 2005 10:08 pm

Yep, fair comment Mike! Trouble is, I'm one of those annoying blighters who
likes to get to the bottom of little technical issues such as this one, and
sort out what's rumour and what's real ... but indeed a man can get carried
away with it sometimes. Still, if getting to the bottom of it saves me from
chucking out expensive batteries for no good reason, it's worth it (and it's
always satisfying to suss something out instead of giving up).
All good fun,
G

------------------------
From: "Mike Jolley" <JOLLEY.HAHA@xtra.co.nz>
Subject: Re: MX5 batteries flattening
put all your energy worrying about the battert into it and you could charge a
fleet of mx5 owners)
tounge in cheek answer

Mike Jolley

MX5 batteries flattening

Post by Mike Jolley » Fri Feb 04, 2005 11:21 pm

Good on ya mate !!!

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