How long should the battery hold its charge

[AJ]

yup, old age is catching up with it mate.

[chatchat]

I still have the original battery, and it only hold 5 days max, trying to find a right battery, but not easy to find the perfect size.

[grump]

should only have to replace battery when it needs it, the battery in the MX5 probably has a longer life span than most vehicles because of its position in the boot. Heat is a big killer of batteries, and the engine bay is normally the hottest place in a vehicle, I've had some vehicles that only get 2 -3 years, and some that get more. My wife's honda still has the same battery from new, 8 years old. I've always found that whenever I have to replace a battery I'm unlucky enough to own a vehicle that requires the most expensive one

[sliq]

if its one of the batteries that require some water to be poured into it, that might revive it for the short term

[mx52nv]

NA and NB MX5s should all use batteries that are sealed and vented (which should hook up to the factory venting tubes). This means they are maintenance free and usually come with a one or two year warranty. Having a lead acid battery in the boot is not a good idea.

If you ask nicely, Mazda Parts (WA - so check your own state) will try to bring down the price to match written quotes for aftermarket MX5 batteries (sealed, vented and similar size). The other benefit is that it will be a 5 minute "drop-in" exercise as everything fits correctly (I think the WestCo is also drop-in for the MX5).

The only reason you would get another brand (i.e. Odyssey/Federal/Optima/AC Delco) is that you need more power and a greater cranking rate (for a big audio system possibly). But my two cents here and when I was doing the Auto Salon circuit and the car would not get dríven much, my expensive Odyssey battery went flat 3 times and required replacing 2 times. These high cranking batteries do not like going flat.

However, the same rules apply and you should still be using a sealed battery in the boot of an MX5.

In regards to the OP, most batteries should hold their charge between 1 to 2 weeks in the least. Some owners may get a month but this greatly differs when there are other current draws like aftermarket alarm,audio & any other electrical/lighting systems that are installed.

[smmax]

Hi Greyhair,

What mx52nv said and...

Your usage pattern is a lot like mine. Mine is original in a 2001 and it is as strong as now.

Don't give up on that original battery just yet. The Panasonic AGM is an absolute beauty if you take the time to understand it. They are not like normal wet cell (Sb/Sb)or low maintenance batteries(Sb/Ca). The charging needs to be "right" for them.

If you check the big US forum you'll find that that you can easily get over 10 years out of the original Panasonic. Not bad, if you consider the extremes of their weather.
The most common "flat battery" discussions seems to stem from additional equipment (like alarms, doof-doof etc) and alternator problems.

The AGM battery has a big advantage over normal wet type in the internal self discharge rate is very low. In the NB the normal "dark current" is relatively small. My calculation is that a fully charged battery will still have enough to start a normal MX5 after 3-4mths of non use easily.

The most important thing to note is the history of the battery. If it has spent a lot of time with a state of charge (SoC) below 75% or less it made have developed a bad case "sulfation". This will directly reduce its capacity. It is sometimes recoverable with use use of a de-sulfation device (http://en.wikipedia.org/wiki/Sulfation).

The important point is not to let the battery sit at less than full charge for any period of time. True for all lead batteries. If the lead is not in suspension, the crystals can not form, therefore no sulfation.

If mine was sulphated, I' get another one exactly the same (Panasonic) and treat it right from the start.

You already have the the key to maintaining your battery. The "Jump Start" unit you have is a AGM or SLA battery in a box with a charge circuit to match. Just what you need. Don't use a "normal" charger , ever. This is important. An AGM battery must never have more than 14.8 volts across it (at a temperature of 10C).

Try this. Place the jump unit across the battery as if you were going to start it and then connect the power pack to the Jump unit. Let it do its full charge cycle. (The jump unit normally has a trickle charge circuit that shuts off at the right voltage, does yours?). It may take a day or two to bring the Battery right up.

Get a Digital Multimeter ($10 from Supercheap, DSE ).
Disconnect the jump unit and wait 12 hours to get rid of the surface charge, then measure the voltage across the battery .

You should see at reading of 11(flat) to 12.8 (100%). You can't read the charge state in a AGM with hydrometer. Reading the "stabilised" voltage will give you the SoC . See http://www.batteryfaq.orgfor a spreadsheet with the SOC against voltage with temperature compensation. If you can't get it from there PM me and I'll email you a copy.

If your battery comes up ok, just leave the Jump unit across the battery and with a 7 day timer (Bunnings $14) to let it top up once at week. The Jump unit assists with the dark current while just sitting. You'll be good to go for years.

I have "hot" plug in the glove box to connect the jump unit to make it easy to connect. I guess if you have a garage queen its a small price to pay for instant start.

[Juffa]

Now for my non-scientific input. My first panasonic battery lasted 12 years, in a daily driver. My current panasonic battery is about 4 years old. It gets fired up on average once a week, but there has been some recent times when it went 2/3 weeks without leaving the garage, and fired up first time. This is with an alarm fitted, so drain would be slightly more than a average NA.


My 2.2 cents worth (including GST).

J

[ASE05]

My car spends most of it's days in the garage with the key in the ignition.....untill recently.

I was forever having to give it a charge after leaving it for more than 2 weeks w/out starting her.

A couple of mths ago I thought I'd leave the key out in the footwell and ever since no dramas. Infact, this thread just reminded me to kick her over and 4 weeks since she was last run, it was a bit slow to start but managed it all the same.