12v Battery Best Practices

[mrdo]

Hi,

As a hopefully new owner of an e I'm trying to do some homework by reading through all of the great information on the forums.

The most glaring potential issue seems to be related to the 12v battery. As my car is likely to be left sitting at home unused for a week on a regular basis, I was wondering whether the general consensus would be to have the car connected to a charger and have it do a small charge every day or couple of days just to keep the 12v topped up?

I would like to install a battery monitor but will not be within bluetooth range so not sure there's much point. I'm not sure the car will have any connectivity as the location is a WiFi and potentially a 4G deadspot too (although the charger itself will have internet access).

I am also considering keeping the auto updated turned off (even though it seems unlikely there will be any more updates!).

Is there anything else I should be thinking about doing? Should I also be considering buying a battery booster? My membership to the RAC has lapsed to I guess time to renew as well.

[Verone]

I had zero issues with the factory 12v battery for close to a year, until like a week or two ago, when I left the lights on and it ran flat.

After that, I decided to change it out for a Yuasa 5053 as a replacement, as recommended by a lot of other owners of the e.

Honestly, if I hadn't been an idiot and left the lights on, I'd still be running on the factory battery now, but then again I've had the car from new, so I know it hasn't been run flat before.

If you're buying a used one, you don't know for sure if it's been discharged before, so it's probably best to just get it swapped out.

[EEEE]

The cheapy BM2 battery monitor is still useful even out of range. It will log/store 30 days of data. You can then 'pick up' the data when you are next near, and have a look. I correlate with my CCTV to work out what happened when and see if I can explain any abnormalities (after a few months of use, I am seeing some unexplained things but we will never know how the black boxes work!)

12v battery charging doesn't happen necessarily when its connected to the mains. The 12v battery is only float charged when the HV battery is charging. Its not even clever charging like a normal digital charger.

If the car is unused for a week, leaving it plugged in for a week will actually slightly flatten the battery (if you get a battery monitor, you will see that after charging has finished but remains connected to mains, there is a little 12v voltage dip every 2 hours (some sort of check / pump run / etc), this does not happen when the car is unplugged).

If you can accept a lower charging speed, charging at the lowest rate (as dictated by the charger, eg 1.2kw), you can extend the HV charge time, and thus extend the 12v charging time (not that the 12v charging is proper, it just floats at 13.3v continuously).

Other advice is to not leave the drivers door open. The car doesn't fully power on until you sit in it and close the door. So if you are showing a bystander the infotainment, or hoovering your car out, these are the times when you might accidently flatten your battery.

The phantom drain - we don't know what causes it. System updates pushed out but no WiFi signal (the update packages are not pulled OTA by TCU, just the notification/instruction) is likely 1 cause but not the main one. Dodgy microswitches or door handle/latch mechanism is likely to be another. Hard to diagnose. I'm still trying to think how I can monitor/collect more data so I am better informed the next time it happens (I have no doubt it will happen again).

Best insurance is to keep a lithium jump pack in the glovebox, and practice using the key to unlock the door and perform a jump. Worth showing to anyone else who uses the car, as sods law it will happen at the worse time (Happened to my wife when she needed to take my mum to hospital, worst possible timing, she now hates the car).

[MaXPainT]

I am still on my factory battery (the car is 3 years old), zero issues so far (knocking on the wood).

I haven't seen any evidence so far that leaving the car plugged in will affect the 12v battery in any way. There are several reports on this forum with 12v batteries dying when the car is plugged in. However, there is some evidence (mostly based on Bjorn's YouTube video) that the 12v battery is charged during the preconditioning of the car. Maybe it would be a good idea to keep the car plugged in and precondition it periodically even if you are not driving anywhere. You will lose a couple of % on the main battery but it will be topped up with the charger. I am preconditioning my car 2 times a day (weekdays) for 20 minutes. I do believe that turning on the preconditioning should be easier for a weak 12v battery than starting the car with all the unlocking, lighting, and computer booting going on.

I don't see the point of buying a battery monitor. It won't help you in any way to see that the battery is dead if you have no means to start the car. I would rather buy a battery booster to start the car when the battery is dead and replace the 12v battery every 2-3 years or after the first time you will have to use the booster to jump-start the car.

[EEEE]

It won't help you in any way to see that the battery is dead if you have no means to start the car.

The cheap BM2 battery monitor connects directly to the battery, and you can pick up via bluetooth the status and history. If you are close enough (not very practical admittedly) it can warn you that the voltage is low.

Aside from any real practical benefit when you have a flat battery - the detail it gives is vital to understanding the 12v system and how it works (and how it doesn't).

[Verone]

The phantom drain - we don't know what causes it. System updates pushed out but no WiFi signal (the update packages are not pulled OTA by TCU, just the notification/instruction) is likely 1 cause but not the main one. Dodgy microswitches or door handle/latch mechanism is likely to be another. Hard to diagnose. I'm still trying to think how I can monitor/collect more data so I am better informed the next time it happens (I have no doubt it will happen again).

I 100% think that the OTA Updates with no wifi signal is one of the prime causes of the 12v battery drain. This and the car being left in accessory mode (the same as having the ignition on in an ICE car).

I've had my e for a year now just about, and in Iceland there's no support for the e-sim and app, so it's just disabled (Honda have said they're working with Vodafone Iceland to set something up as more cars that will use the MyHonda+ app are sold). Whenever I want to have the car connected to the intertubes, I use a WiFi hotspot from my phone.

I've never had 12v battery issue until I screwed up and left my lights on, and at one point last summer, three months after I bought the car, it was stood for seventeen days while I was on summer vacation. No 12v issues when I got back, and after all that time it'd lost 2% charge from the traction battery pack.

I absolutely think that the internet connectivity when the car is stationary and powered off is one of the culprits here.

Other advice is to not leave the drivers door open. The car doesn't fully power on until you sit in it and close the door. So if you are showing a bystander the infotainment, or hoovering your car out, these are the times when you might accidently flatten your battery.

This is a huge one, totally agree.

Never leave the car with accessories only on, without it being fully powered on. This will kill the battery for sure with it having to power all the accessories and all those screens from just the 12v.

This is also a prime cause, and there's been lots of stories of people being at dealers looking over a car and it going flat on the forecourt because of this while they're fiddling with features.

Typically whenever I have the car stood still and I'm working on it - cleaning or washing it, I make sure the driver's seatbelt is plugged in, this tells the car not to shut down into accessory mode because it's occupied, and instructs it to keep charging the 12v from the traction battery.

I'm actually thinking of buying one of those belt buckle alarm stoppers just for this, so I can leave the belt unplugged and just slot that in when I'm washing the car or cleaning the interior.

[FDAD]

I'm actually thinking of buying one of those belt buckle alarm stoppers just for this, so I can leave the belt unplugged and just slot that in when I'm washing the car or cleaning the interior.

I can say with certainty that the system will charge the 12v even in accessory mode.
I thought that wouldn't happen but i have see it multiple times with a battery monitor.

[MattHero]

All good stuff, thanks all!

I too am on the original 12v and so far, it's holding up. I've always judicious in pumping the brake the moment I get into the car, to switch on the traction battery (the doubled ended green arrow on the dash), even if I'm not planning to get anywhere, so maybe that's been my savour?

Certainly, right now with the car sitting waiting for my dealer appointment for the brake issue, I've been going out for 30 minutes a couple times a week to sit in the car to (hopefully) top up the 12v a touch, so that it doesn't flatten before I take it in to be looked at. I realise I could plug the belt and leave it, but for some reason I still like sitting in the car and reminding myself that it is actually a nice environment to be in.

[mrdo]

I too am on the original 12v and so far, it's holding up. I've always judicious in pumping the brake the moment I get into the car, to switch on the traction battery (the doubled ended green arrow on the dash), even if I'm not planning to get anywhere, so maybe that's been my savour?

This is what I had also meant to add - I guess I'd rather lose a little bit of charge from the main battery rather than have a flat 12v battery.

Does anyone know if something like this would work?

If so, it would be useful when I go to buy the car and also to monitor the 12v when in the car.

https://www.ebay.co.uk/itm/386282154950

[EEEE]

That battery monitor is useless - for just a few quid more you can get the BM2 which logs 30 days minute by minute.

I'm pretty sure the charging only starts when the drivers door is closed. I think if you open the car, sit in, press the power button, put the seatbelt on but don't close the door, the 12v charging will not start.

The last time I went flat was outside halfords whilst loading in a couple of batteries and chatting to the staff members and another forum member. I made sure to plug in my seatbelt, but the drivers door was open. I'll check tomorrow actually as the BM2 also shows real time voltage with better resolution than the 24h overview screen....