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Discussion Starter · #1 ·
Perhaps some of you are concerned about what happens to HT & LT batteries if you cannot use the car for some time. Well, I left mine standing for 5 weeks and 5 days and here is some of the information that I have gleaned.
I left the HT battery at 73% state of charge (as per instructions to leave it some way off full charge) and I made sure that the 12 volt battery was fully charged with an external charger. The average temperature over the period would have been about 14C so no high or low temperature issues. On my return, the car doors unlocked with the remote and everything operated normally. I raised the bonnet and checked the 12 volt battery and it was down to 12.01 volts. So I put a charger onto the battery and an 8 amp charger needed some 2.7 hours to charge. That doesn't quite necessarily mean a simplistic 2.7 x 8 = 21.6 Ah but it does mean that the little battery took a lot of charge. After charging, the battery voltage measured 12.86 volts after a couple of minutes.
Now for those of you who don't want to read the next paragraph of numerical ramblings, please just go to the conclusions. For those of you who like detail and perhaps can help me, here is what I did next. I drove the car for 20 minutes and then returned home but left the car in "Ready" mode. I measured the charge potential at the battery as 14.14 volts. Then, I pressed the stop button and the battery voltage decreased for a little over 2 minutes to 12.45 volts. (The water circulating pump was definitely stopped!) With nothing apparently happening, the voltage then rose to 12.68 volts until there was a clanking of relays about 4 minutes from stop. Then the battery voltage went up quickly to 12.78 volts. This held steady for about 9 minutes until more small relays were heard and the voltage dropped again over a minute to 12.35 volts (I am lost as to what was happening). I gave up at this point and locked the doors with the voltmeter still on the battery and the voltage went down further. So, I tidied up from everything that I had been doing and went back after 10 minutes or so to remove the volt meter and close the bonnet. The battery was showing 12.76 volts!
So, I conclude the following.
1. Left in a temperate climate, long term storage of the HT battery is not an issue. It would appear to lose much less than conventional wisdom of 3%/month. Of course, battery heating in very low temperatures is not considered in this post.
2. The 12 volt battery cannot be left for months. I don't know the minimum voltage at which the 12 volt system can no longer pull in the HT breaker or open the door locks but I suspect that mine could have been in trouble after another couple of weeks. So, it's battery disconnect or trickle charging if one wants to leave the MX-30 for months. I know that 5 weeks and 5 days was OK but??????
3. The more I learn about this car, the less I seem to know. If anyone can cast some light on what is going on, please enlighten me. There is clearly all manner of electrical use occurring for 9 or 10 minutes after one presses the stop button!
 

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Dear Milkfloat,
What was the SOC of the main battery on your return? Or perhaps you already said? 12V batteries, dont get me started. Its been drained in the id3 a number of times. But VW insists its in great shape. The id3 spends more time at the dealers than at home lately. Never been an issue with the Mazda. In this country id3 drivers are a miserable lot, in surveys and I know one pretty damned well. MX 30 does a lot better. What good is an impressive range and all kinds of modern tech if it aint working? End of rant.
 

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Discussion Starter · #3 ·
Stupid omission, thanks for pointing it out. The HT battery was 71% SOC so just 2% lost. I know that the ID 3's are struggling with the 12 volt battery as the Leaf has done in the past. From my little exercise yesterday, I conclude that there are more demands on LV system than we perhaps understand. I have left ICE cars for similar times and the battery has lost much less. Though the MX-30 doesn't appear to have a major issue with the 12 volt battery it is worthy of a little care. I hope you get the VW sorted out; your rant is understandable. When a car won't start, it fails in its primary purpose.
 

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Maybe just been lucky w the Mazda dealer. But they are the most customer oriented dealership I ve ever come across. Friendly, professional and easy to get in touch with. BMW, the dealer has a spotless interior fancy pancy. But if you look beneath the glossy surface Mazda customer service wins hands down. Is this local, coincidence? Dont know. Are you guys happy with your Mazda dealerships?
 

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Again really valuable information for the future, I suspect the 12v battery is the cheapest part of this car and as such may be it's achilles heal in the future, but if this becomes the case I have faith that Mazda would replace the batteries with better alternatives, or we will do it ourselves if the need arises.
As for my Mazda dealer here in Anglesey North Wales, I can't sing their praises enough, they are very helpful, not pushy and seem to get things done quickly and efficiently which my brain loves 🤣
 
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