How Long Does The Battery Last?

Saturday 14th March 2015

How long does the battery last? This is one of the questions we are asked the most often from people when we are out and about showing off our Electric Cars – I think that they are really asking, How far can you drive on a single charge?

As we’ve found out over the years there really isn’t a definitive answer. The range on the cars guess-o-meter will give you an idea but after many drives we have found that it is all down to the way you drive the car. Drive nice and gently and you will get more miles out of your battery, drive fast and you will see your miles disappear at a rather quicker rate. I would say it is one of the more difficult questions to answer accurately.

One day three years ago we decided that we should test the theory out with our 2012 BMW ActiveE. You know, just to see how far we could drive on one charged battery. Here’s what we found.

We planned a Sunday afternoon drive with the ActiveE, going out for a fun drive rather than driving for necessity, even though driving the ActiveE was always fun regardless. We wanted to see how well the battery did and what kind of mileage we could actually get. The weather didn’t look good when we awoke to fog and rain on the Sunday morning, but we’re British, after all, so that wasn’t going to stop us. Fortunately by the afternoon the rain had stopped and the sun had started to make an appearance so it looked like our drive would be rather pleasant.

We set off with my Sidekick adamant that he knew where we were going, he said that he had a drive all planned out. Jolly good! Although, we had only been driving for ten minutes when we had to stop and switch on the Satellite Navigation as he suddenly wasn’t quite so sure anymore! Hmm – It turned out that we had already gone the wrong way! A good start. With the car now going in the correct direction, we settled back to enjoy the drive and take in some new scenery. The day was warm enough that we could turn off the HVAC, so we were able to drive along so silently. The HVAC is actually quite noisy, I guess that this is what happens when you don’t have an engine drowning out everything else, you actually hear things that you wouldn’t normally hear in a petrol car.

The range remaining display on the ActiveE seems to be quite true to what it says, it does seem quite stable. Often when we first get in the car in a morning the difference between the range reported in regular mode and Eco mode is quite significant, there can be as much as a 12 mile difference.

The ActiveE has “Eco mode”. When you engage “Eco” the car reduces the sensitivity of the accelerator and reduces the power to the HVAC. This encourages you to drive more gently and reduces the heating and cooling power demands. Basically, you give up some comfort and fun for more miles.

We had left home with 98% charge (it was still charging when we unplugged it) and we had an approximate range of 80 miles in regular mode, and 96 miles in Eco mode. We ended up driving over 80 miles that day and still came home with 16 miles to spare. How could that be? Well, we drove for about four hours, most of the driving was on 35 mph roads with the odd 50 mph blasts thrown in and the occasional slow 20 mph road. As we drove very economically, the car began to re-evaluate the available range. When we checked the battery level it had climbed from the starting point of 80 miles up to a 96 mile range in regular mode, hence the 16 miles still remaining at the end of the day. So, if you drive gently you can really get quite a few more miles out of your battery and its predicted range will go up. The predicted range looks at how you drove the car the day before and guesses how many miles you will get out of the battery determined on the previous days driving. Which is why I would always see a higher predicted range than my Sidekick would – Just saying!

It seemed that on our drive, that by driving gently in regular mode, the difference between the regular mode estimate and the Eco mode estimate had converged. At one point during that day, at 50% battery, it was only a three mile difference. This makes us believe that it is all down to the way the car is driven… drive gently and you get almost the same amount of miles in Comfort mode as you would in Eco mode. Driving on the motorway, the miles go down quicker due to the increase in speed… the faster you go the more energy you use – it’s all down to the wind resistance.

We really enjoyed just driving that day, it made such a change from our usual day to day planned driving. We didn’t have to be anywhere in particular, there were no children to be dropped off or picked up, no time constraints… it was driving just for pleasure. We’d rather like to be able to do this more often, but alas work and life seem to get in the way!

Next time we do this it will be in the BMW i3, but we’ll wait for the snow to go and the roads to be a bit better and see How long the battery will last!

Oh, and to answer the question How long does the battery last? Well we haven’t got a definite answer as there are too many variables to take into account but on that particular day it latest at least four and a half hours.


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