# Battery Bleed Off



## rushbikes (Feb 5, 2012)

Hi everyone, new to the forum. Am looking at picking up BMW's new EV, the ActiveE, and was wondering if it's typical for EV's to experience battery bleed off. That is to say, if I fully charged my ActiveE and left it unused for a month, would the batteries remain fully charged? Haven't been able to get a direct answer from BMW or two local dealerships.

Also, is there any negative impact to leaving the EV plugged into my charging station for weeks? I'm not familiar with charging stations & EV's, but presumably they have an auto shutoff when the EV is fully charged.

Any downside to using an EV infrequently? It will be a second car, used about every other week. Occasionally more infrequently.


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## Ziggythewiz (May 16, 2010)

Yes, all batteries will self discharge to some degree. With lead acid, it can be high where a month is bad and a few months can destroy them. With lithium it depends on the chemistry and the setup, but should be fine for anywhere from a month to several at least. 

Downsides to staying plugged in depend on your setup. Say power goes out for a min, what happens when it comes back? Does the charger go back to what is was doing, or try a new charge cycle? Also, what does a power surge do? 

The primary downside to not using EV frequently is there is no ROI for an EV sitting in a garage. For an EV to be worth the money, it needs to be used regularly. If you have the money, and aren't concerned with a ROI, EVs are great for infrequent use. There's no gas to foul, no (or less) fluids to leak or worry about, and the motor doesn't need to run for an hour to get back in shape after sitting for a month.


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## rushbikes (Feb 5, 2012)

Great points. I'm unsure how BMW's charging station works but I'll try to find out more. I suppose I should also confirm BMW/insurance covers surge damage.

Anyone aware of instances of surge damage? Would a serious surge fry all the electronics incl the motor? Batteries?


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## steven4601 (Nov 11, 2010)

Best would be to ask about the maximum standby (off-grid) time for the vehicle. Quite possibly it will be months, but ask an (certified) active-e dealer for clarification.


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## Ziggythewiz (May 16, 2010)

Also ask if there's a user friendly way to disconnect the battery. There are always parasitic loads that will drain it faster than if you can unplug it.


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## dougingraham (Jul 26, 2011)

rushbikes said:


> Anyone aware of instances of surge damage? Would a serious surge fry all the electronics incl the motor? Batteries?


The batteries make a pretty effective buffer between the outside world and the car electronics. A surge could be expected to cause damage to the charger, but not any of the rest of the car's electronics. A lightning strike on your residence is a different thing entirely. It could cause damage to any electronics that are plugged in including the car. You can protect against it but lightning does what it wants to. If the car is plugged in it would be vulnerable.

However these are reasonably rare events. For example ask yourself how many TV's have you lost to power surges? It is less likely to affect the EV battery charger than a TV.


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## dtbaker (Jan 5, 2008)

Li batteries without parasitic load have a very low self-discharge... much lower than lead for instance. HOWEVER, if there is an 'always-on' load from a dc-dc convertor, clock, etc the parasitic load might be higher than you might guess.

so... if you are going to let an ev 'sit' for more than about a week you need a way to disconnect the pack from any parasitic load.

most DIY designs have a big fat circuit breaker between pack and all other loads; just flip that off, and you are good. OEM builds I don't know....


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## GizmoEV (Nov 28, 2009)

I seem to remember someone saying that the Nissan LEAF had a "storage mode" that was selected when it was going to be parked for an extended period of time. IIRC, it was to be plugged in during this time but that the battery didn't get fully charged to prolong its life.


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## rushbikes (Feb 5, 2012)

GizmoEV said:


> I seem to remember someone saying that the Nissan LEAF had a "storage mode" that was selected when it was going to be parked for an extended period of time. IIRC, it was to be plugged in during this time but that the battery didn't get fully charged to prolong its life.


Yeah, I've been posting over in the Leaf forums as well, and I'm not sure if it's called storage mode, but there is a mode that charges to 80%. The Leaf also uses a mobile app called Carwings that allows you to start, stop and monitor charges. Pretty neat in theory. I'm told it doesn't work terribly well in practice.


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