Relationship between battery pack and time to recharge

[voyager]

To what extent is there a (linear) relationship between battery pack size (and of course weight) and the time it takes to recharge? Let's for instance, consider the Jaguar i-Pace with its 600 kg battery pack and the BMW i3 that has 250 kg of batteries on board, both using the same charger.

 

[ewoodrick]

To what extent is there a (linear) relationship between battery pack size (and of course weight) and the time it takes to recharge? Let's for instance, consider the Jaguar i-Pace with its 600 kg battery pack and the BMW i3 that has 250 kg of batteries on board, both using the same charger.

When talking about battery capacity, you should be talking about watts or amp-hours. Weight isn't the best judge when talking about capacity, as there are batteries that hold a specific capacity and are lighter, and batteries that heavier. The difference is often price. For example, the batteries can be heavier and cheaper in a semi, than an airplane where every once counts.

Once you choose a capacity, then the charging performance of the different packs can vary. They may vary from numbers like 0.5 of the maximum battery per hour, or 1.5 times the maximum capacity per hour. And yes, again, the difference often impact the price, the longevity, and the weight

The batteries chosen for EVs have similar profiles, but not the same. A lot of research is going in to batteries that can charge fast. And to confuse things even more, the chargers also often limit the amount of charge that can go into the batter.

And to keep what seems to be a simple subject more complex, very few batteries can take maximum charge across at all charge levels. Most batteries accept maximum charge only between 20 and 70 percent. Going from 70 to 100 percent can often take as long as going from 20 to 70 percent, because of the slower charge that the batter will accept

So, let's look at a vehicle with a choice of 40kWHr battery and an 80 kWHr battery. It's basically a very linear relationship. It's going to take twice as long to charge the bigger battery.

 

[animorph]

Depends on too many other factors I think.

However, best practice would be to have a pack that charges fully in the time it takes one individual cell to charge. In that case, given an appropriate charger and charge rate, any pack size would charge in the same time.

If the charger is really low power then of course it will take a longer time to charge a higher capacity battery, and I would expect the charge time to be fairly linear with capacity.

In between, maybe the manufacturer hasn't allowed for fast charging, or selected a battery chemistry that cannot be charged as fast. So kind of hard to say.

I bought the X100D because it would charge X miles to reach the next Supercharger faster than an X75D, which is the time that really matters to us. The same rated miles range is reached at a lower state of charge for the 100D and thus less time is spent in the charge taper region. In that sense, higher capacity batteries are quicker to charge than lower capacity batteries.