Why the "Recommend 80% Charge"?

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Texalian
Posts: 4
Joined: Mon May 17, 2021 4:36 am

Post by Texalian »

VW Recommends charging only to 80%. "Recommend" isn't the same as "Charge only to 80%".

Does anyone know why the recommendation to 80%? Makes no sense to me.

markkernw
Posts: 6
Joined: Fri Apr 30, 2021 3:18 pm

Post by markkernw »

80% recommended charge relates to daily commute usage of the electric vehicle because you probably don’t need 100% full battery for day to day running around.

It’s been found that perhaps 60% daily charge (if that suits your usage) is best for optimal battery life. But I charge to anywhere between 60-80% depending on what I’m doing the following day or two.

A number of considerations about the car (any) Lithium batteries :

1, for long journeys of course take that charge up to 100% before you start. Says so in the manual. Gets you a bit farther before you need to find a charger on your journey. Maybe 100% will get you to your destination which hopefully has a charger you can use while you eat, sleep, rest :)

2, if you use a rapid charger en-route of a really long journey - so you charge when having a break - you really don’t want to charge beyond 80% because the final 20% of charging between 80-100% takes almost as long to charge as initial the 10/20-80% rapid charge (the 77kw ID will rapid 125kw charger up from 10/20% up to 80% in 35-40mins I’m told. ) it’s down to the battery management software and the fact it’s easy to push massive volts into a near empty battery as there’s loads of space to just throw it in pretty much randomly at speed. Less for the battery software to ‘manage’ when it’s simply throwing all the volts at anywhere in the battery pack, so to speak. Remember the battery pack is a series of many smaller battery cells each being charged. But as it reaches 80% of charge, now the battery management system has to closely analyse which individual battery cells in the pack need more juice and which do not, controlling where the flow of electricity is sent. So it slows charging down because it’s effectively micromanaging the last 20%.

You’re wasting your time hanging on for the last 20% up to 100%. You make better use of your journey time stopping again at about 10-20% charge left and using another rapid charger for around 35 mins. There’s videos and articles online that attest to this.

3, you want to leave some ‘spare’ battery capacity to give the motor braking regen somewhere to put that regen charge. The car will regen on braking at the very least. If you leave some spare battery space for regen charge to go that’s a little bit of free power as you drive along.

4, by always taking the battery up to 100% every charge you deteriorate the battery cells faster than taking it to 80% usually. I don’t understand the science but it’s something to do with the battery chemistry that responds better to not being rammed full of charge on every recharge. So 80% charge helps your battery hold that golden mileage range for more years of its life.

In terms of general maintenance it states in the manual something about not letting charge drop BELOW a certain % for leaving parked up for a time (worth remembering when we can fly on holiday again and you park your ID in an airport car par! , particularly so in cold weather as i believe VW have programmed the main drive battery pack to donate charge to the small 12v battery that’s required to get the car open and systems startup before the main battery adds its load. The car I think must monitor the 12v battery to ensure it doesn’t fall below a level at which you won’t even get the car open never mind start it up. Not sure how that all configures. I’ve failed to find much information on specifics. Like many things VW seem to keep a lot of info & explanations to themselves and it’s only the curious and helpful that dig deeper and find some answers. Even the technician at my local VW knew less about the car than I do now and he’s commissioning and servings their ID range!

Hope that’s of some help :D
CoxJul
Posts: 64
Joined: Tue May 04, 2021 6:14 pm

Post by CoxJul »

Pretty much covers it!

If you checkout the ev-database page (https://ev-database.uk/car/1273/Volkswagen-ID4-1st) you'll see the charge curve showing the drop-off over 80%. Matches my experience on an Ionity charge on a good day. Approx 30 mins 20-80%, another 30 mins for 80-100%! Of course, if you're having a leisurely lunch on a long trip then go for 100%, little harm if you're about to use it.

For regular short journeys between 7kw topping ups at home, taking it regularly to 100% may cause long term issues.
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