Battery Resilience

I last used my 2010 2.0 Sport Tech PRHT on Xmas Eve and then washed it before moving it across the drive - so a fairly full charge followed by a quick start up and re-position. 11 days later, I checked the battery and it was about 11V and just turned the engine over and caught, so I gave it a 20 minute run out. Alternator is good pushing 14V on a run and 13.9V at idle. 

Ive put in the garage as it’ll be easier to stick a charger on under cover (Aldi smart charger) but I’m guessing the battery is probably in need of replacement. To complicate matters, I’m going to be away for 6 weeks in summer so do I replace the battery now or hang on until summer and replace it when it dies it’s natural death. 

Im unwilling to leave it on a conditioner charger as I’ve had bad experiences of a dead cell overheating before. My old Copen with a replacement 40Ah battery managed at least 3 weeks but I’m not sure how long an MX-5 should last.  

Whats the collective advice ? If it’s battery change, when and for what ?

Assuming original, the battery will be at least 8 years old which is a reasonable lifetime expectancy for this battery. I would try to keep it going as probably halfway through the cold winter.

Irregular use does not help and I would drop your misgivings about the conditioner charger - it is the only way to look after these batteries when not in regular use.

Hopefully you can eak it out until the 6 month holiday but in any event this is a recommended replacement.   

Thanks for the advice.

Up until Christmas the car was in very regular use, to the point that I had to increase my mileage for insurance. Once I got it all nice and clean, I was reluctant to use it much on salty roads as it’s in very good condition underneath and I’d just PX’d the BMW for the new Vitara.

Unfortunately, the link to the battery replacement may be expired but I’d like to go OEM even if it costs more. How long should I expect a brand new one to hold a charge without being driven ?

I can only give you what in my opinion is the best advice Rob; it is your prerogative to take that advice or ignore it:-)

The link still works for me but by all means buy an OEM battery if you can source it but expect to pay at least double the cost of the one suggested. It is a panasonic lead/acid from memory, not the much longer lasting AGM Panasonic battery used by the earlier MK1 - MK2.5 cars. Quite a few get confused with this. Eight years for a small lead acid battery is really on the margins of life expectation but you will notice, when you get that link to work or alternatively just look up YBX5053 on ebay that the battery I recommend has a 4 year guarantee.

MK3.5 would have considerably higher parasitic current than the earlier cars, so periods unused particularly in the colder weather will add unreasonable stress to any battery let alone a lead acid variety at the end of its useful life. Given your situation I would regularly check the battery voltage and charge it when the voltage drops below say 12.3 volts.                 



Hi Rhino,

I’m a bellend. I saw the ads above the listing and assumed the original listing has expired (don’t use the site that often).

I’m with you on the battery life - 8 years is good and charging advice.

I had a similar issue on the Copen and it turned out to be a ruptured cell that prolonged charging could have turned an inconvenience into a real humdinger; hence my reticence. I’ve no problem charging on an ad hoc basis but the wife’s brand new 6 is in the garage and I’d never hear the last if a cell blew on the defunct MX-5 battery. My hope is to tickle it at or around 12 volts and change it after the holiday. I’ve used the key to lock the doors so it’ll reduce, but not eliminate, the parasitic draw. If I can stretch the renewal until after the hols it just saves an extended drawdown.

 I also have a 2010 mx5.  Thinking back to when the car was a couple of years old I remember that if I left the car in the garage for 3 weeks I could start the engine but at 4 weeks I had to jump start or recharge the battery to start the car.

I still have the original battery fitted and have an Aldi auto XS to maintain the charge. I think for peace of mind that I will fit a new battery when I start to use the car this year.



Given that a battery is going to last some considerable time, possibly beyond the life of the car or your ownership, why give yourself the hassle of trying to keep and old battery charged, you are going to spend the money anyway. 

Buy the new one and take the stress away. If you are worried about discharge then just leave the battery disconnected until such time as you plan to use the car. You are going to be disconnecting it anyway to fit the new one. 

You can never have enough battery chargers


My Mk3’s battery prematurely expired i reckon at just 8 yrs old, if I’d kept it maintained over winter it could have lasted a little longer. My daily driver battery was deemed low on power back in September last year throwing up all sorts of fault codes. A new battery fixed it, that battery was less than 5 years old when replaced, lack of use (car)  and lack of maintenance of the battery deemed the cause. 

I’ve had both batteries on charge this winter hence the two chargers, an Aldi and Lidl  special.

I don’t claim to be an expert, but I took the trouble to find out about batteries when I was using (and as it turned out, abusing) expensive leisure batteries in boats.

  1. Lead acid batteries in general aren’t resilient to being discharged repeatedly below 50% charge state, which will reduce capacity.  Car starter batteries only last 8 years or more because most of them stay fairly fully charged.  

  2. As you probably know, trickle charging is not the same as using a proper maintenance charger which will pulse charge when the battery is ‘full’, although ‘full’ might not equate to a normal full charge if it is near the end of its service life - it sounds to me as if the capacity of your battery is already much reduced.

3.  Measuring voltage might not be the best way of assessing the state of charge when there is even a small drain (which drops the voltage anyway) but 11V is well down and, in practical terms, flat.    If you disconnect a healthy battery to get a reliable reading, when ‘settled’ after charging, a voltage of 12.7-12.8 indicates full or near full charge.  12.2/12.3 is about 50%.  Around 12.0 is c. 25%.  

4.  I agree with NickD, replace as soon as convenient.  It is far more likely to let you down when temperatures are around zero anyway.

If you have a car that can stand unused for several weeks it is a good idea to use a maintenance charger to ensure the charge level does not regularly drop below 50%.  If the car is outside or in an unheated garage, it is also worth bearing in mind that a flat battery can freeze at a much higher temperature (just a few degrees below) than a fully charged one, which basically won’t freeze in the UK. 

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All batteries lose capacity (ie how much charge can possibly be stored) with time, even if the cranking ability remains sufficient (CCA).  It simply means that it will flatten sooner, but when charged will still happily start the engine. 

So how can you tell if it needs replacing?

Use a genuine Smart charger that backs off approaching full (for battery to stay cool) and then cuts off when it thinks the battery is charged, and feel the outside of the battery every now and then to check it is still cool.  A Smart charger will not overheat the battery. Cool is important, barely warm is OK, hot is bad. Icy chilly cold when beginning the charge is also bad.

Now the critical bit, when using the Smart charger:

  1. An old battery will soon charge to “full”, because a reduced storage capacity is quickly filled. (Think tea-cup.)

  2. A good new battery, but flat, will take ages to refill, and still remain cool, and in fact the longer it takes the better. (Think 5 gallon bucket.)

The formula is simple, Charge Rate (Amps) multiplied by elapsed time (Hours) gives us the amount of Charge (Ampere-Hours) it is actually capable of holding.

So a good 48Ah battery with a 3Amp charger will take 16 to 17 hours to full from flat before the Smart charger will have backed off to the lower rate and eventually stop.  And it should remain cool throughout this time if the charger is any good.

NC dark current averages somewhere around 28mA (measured on mine), it varies a bit but not significantly, and this not immediately the case (housekeeping functions go on for a few minutes, no idea what it is doing) but certainly from half an hour after switch-off. Assume a (convenient for the sums) worst case of 41.6mA, then the 48Ah battery will take 48 days to go flat (7 weeks), and more like 10 weeks in reality with 28mA.


I fitted a Yuasa and chose the YBX grade in the 5000 series in the 053 case style, ie a YBX5053.  At the time MDS had the best price and quickest delivery.

See my post with pics here


Bought my Mk3 2008 a few months ago, has gone from regular use to weekends only and kept needing to jump start it.

Took Rhino’s advice re the Yuasa 5000 - bought from his link and very happy with the result .  Had a 9v DC transformer holding the settings during change.

I was pretty impressed that the (presumably) original Panasonic battery had lasted for over a decade!



Thanks for the advice everyone. I connected up my Aldi XS charger today as the voltage had fallen to around 12V since the last run 4 days ago. While I was hooking up, I had a quick look and it definitely seems to be the original battery based on BMG’s post above, so I may as well bite the bullet and invest in the new YAUSA battery as recommended.

My only reluctance was that it’s going to be laid up again in spring for 6 weeks but all being well, it should be warmer so not discharge quite as much.

And, like a muppet, I managed to break one of the clips on the battery cover !

out of interest, are the straps integral to the old battery or will they transfer to the new one ?


The straps will fit around the new battery as they are a loose fit around the original. You won’t need them though as the Yuasa should have integral carry handles.

Blooming Nora. How come a replacement battery cover is less than £29 new from MX5 Parts but £41 on eBay. What am I missing ?


If you unhook the terminals it will easily last six weeks just pop them back on when you get back…New Suzuki’s advise to remove terminals on anything longer than two weeks


They can’t have a problem with the ECU needing to re-set as some “5s” seem to then.


Can’t do otherwise your two weeks holiday would be ruined sat in a car park for twenty minutes at tick over at…