Do EV batteries discharge over time, even when not in use?  IE
Yes. All batteries do. Electricity has an urge to travel, even through tiny particles of dust or humidity which may provide a “connection” between its positive and negative terminals.  Â
EVs have a small additional urge, because they are always “in use”, even when the motor and all accessories are turned off, because they have a number of “stand-by” functions.Â
They are listening, even if they are not talking. One of those functions is the battery monitoring itself, for heat, and it will use some power to monitor that and turn on remedies if necessary.
The simplest solution if you are putting your EV in some sort of long-term storage is to leave it plugged in. The charging system should regulate what it uses – it will only draw current if it needs to so its overall consumption on your power bill will be negligible.
The rate of “no use” discharge will vary according to the type of battery, and its own and surrounding conditions. Typically, in EVs it might be 1 percent per day and in optimal circumstances (including minimal standby settings) could be as little as 1 percent per week.
The same general principles apply to the lead-acid batteries in cars with petrol or diesel engines. For long-term periods of no use, you should make sure the battery box, and its cables are clean and preferably disconnect at least one of the terminal cables. There could still be some leakage from dust and humidity between the terminal posts.
An extra precaution, or an alternative if you leave the terminal cables connected, is to make arrangements to run the engine (and hence the charging alternator) for a few minutes about once a fortnight.Â
Once a month will probably be enough if the vehicle and battery are in good condition; more often may be advisable if either the car and/or the battery is/are a bit…dilapidated.
If your car is “VOR” in a workshop for an extended period, make sure the mechanics disconnect (or remove) the battery and keep it regularly charged (all should but few will do that unless you insist) …or prepare to add the price of a new battery to your repair budget quite soon after you get the car going again.
The plates of a battery that is left in a discharged state for a long time will partially but permanently “sulphate” and will progressively decline from full recharge capacity to less and less and eventually nil.
Obviously, the care of batteries in an EV is a very much bigger issue than in conventional cars. In fossil fuelled cars there is usually one battery weighing about 20 kilos.
In EVs the entire floor is covered in a more expensive type of batteries collectively weighing about half-a-ton at more than ten times the cost. They are by far the heaviest and most expensive component of the vehicle.
