Filling the gaps, charging at 25, 30 and 35 °C results in these usable battery capacities

I showed a graph in a previous article here talking about the noticeable difference in range and usable capacity after a series of charges where only the battery temperature was variable. Well I completed most of it now. Just by riding to work and checking numbers in between.

Now obviously I can’t easily control the temperature of that massive battery nor the weather. Previous tests, executed during winter, revealed that it’s really just the battery temperature that influences this end result. And since this battery pack isn’t cooled actively there are ways to heat it up fast… with DC fast charging for example.

That’s how I recently registered that 40 degrees Celsius battery temp charge session. It was around 20 degrees outside so I charged it up fast and then rode it home fast on the highway. Because continuous high speed riding is another good way to get the battery temperature up.

After a balanced AC charge at home I already got less Watt hours to use compared to the 20 and 25 degrees scenario’s. Not a big surprise as 40 degrees is already less than ideal and the battery shows orange instead of green on your dash to remind you. In case you’re wondering, most of these batteries prefer to be somewhere between 0 and 45 degrees Celsius for charging and a wider range for operating temperature.

So next up was to test the same at 30 and 35 degrees. I suspect the optimal temperature to be either 25 or 30. It’s not really easy to achieve this exact temperature so I would only make this effort when it’s really cold outside and you know you’ll need to stretch the range. Otherwise it’s simply not worth it.

To my surprise I never got to see the 16,4 kWh capacity that I’ve seen in the past. Can’t tell if that is because of other parameters I don’t take into account here or that my battery is already somewhat degrading. End pack voltage is always 333,3 V and cell voltage is 4,15 V. Even changes in firmware versions could result in differences so not really something I can verify myself.

Another surprise is how close all the end results were for the rather wide range of 20 to 35 °C. That is especially great news for cold weather riders cause you get the battery easily within that range just by riding fast on the highway, even when it’s freezing outside. So despite the lack of active battery temperature control you should be fine, unless you live in a hot climate.

Getting the temperature down has proven to be difficult. Looking at the batteries the black side panels, easily the biggest surfaces on the battery box, aren’t even thermally connected to the cells. So the only cooling you get is really from the frontal area. The back is almost getting no airflow and right next to the oil cooled (or if you have an EMCE a liquid cooled) motor. Top is covered by a plastic tank cover and has the inverter next to it. Bottom might be getting the best airflow.

4 Comments on “Filling the gaps, charging at 25, 30 and 35 °C results in these usable battery capacities

  1. Have you ever unscrewed the black side panels?
    I haven‘t yet but I wonder if it is possible to thermopaste them to the housing (if there is one).

    1. No haven’t removed them yet. Looks like those are sealed with something black. I only figured they aren’t thermally connected since they don’t get near as warm as the battery temp. While the silver front does heat up together with the battery.

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