eVe V Battery life


When it’s connected, the battery is reecharged from V, so it only consumes more. Or the same, if the battery is full.

But then it uses Bluetooth, so again consumes more power.


By the way, does anyone know which video player was used?


Bluetooth 4.0 maxes out at 15mA current draw. I don’t know the draw from the keyboard+trackpad+backlighting, but I expect it might be more than the less-than-15mA of the bluetooth connection. Because of this, I assume that if the load from the V battery for these components was removed and replaced by a 15mA max, it would reduce the battery consumption of the V itself. If you have some more concrete numbers on the power usage of keyboards, trackpads, and backlights, please share them as I cannot find consistently accurate claims in my own research.

As for when the keyboard is plugged in, the most efficient way to use battery capacity would be for the keyboard to run off of internal power at least for the lighting if not the other components as well, to a certain battery level. It could be set to only recharge when the V is recharging, with the expectation that the V battery will run out before the keyboard. I do not know what if any lengths Eve has gone to balance this dual battery setup, hence my shortened explanation “might consume less power over all, or just less while disconnected from V”

If you do have information on the low-level component power management of the V, please share. Guesswork in this area can only go so far with what is known about standard components of a custom hardware accessory.


If one considers V-battery life disconnected from V-use he has to live with gathering highly variable results. :scream:
His own mindset then decides if he chooses the higher or the lower end of the results. :smile: :rage:
Kind of emotional view, not rational, not scientific. :innocent:


What voltage? This number alone means absolutely nothing.

Then you wouldn’t be able to use the keyboard wirelessly unless you recharge V too. The way it’s currently set up is the best. It recharges the keyboard whenever it’s connected. That way you’re able to use the keyboard wirelessly as long as the tablet is running. So for example if with your use the tablet lasts 8 hours and the keyboard only 3 hours, in your suggested scenario you would pretty much be unable to use the keyboard wirelessly for 5 out of 8 hours. You would have to keep recharging it.

I had some numbers somewhere at home, I’ll have to look for them when I get back home. I will share the result if I don’t forget…


That again depends on design parameters that I don’t have access to. On average 3.3V, but different devices use different voltages. The number doesn’t mean “nothing” though as you would suggest. Specifically it means that at the top end for voltage (3.6V), assuming the ludicrous scenario that the keyboard is sending a constant stream of data, the Bluetooth microchip in the V will max out at less than 50mW. There is a range to this though, depending on that chip it could max under 30mW, and normal keyboard data transfer rate could on average consume less than 10mW.

But we’re getting too far into the nitty gritty. This is a comparison point. I think it’s a valid assumption that the keyboard uses the same if not higher voltage than the Bluetooth microchip. If the Bluetooth chip uses at most 15mA, the only way for the keyboard nominal power usage to be lower is for it to consume significantly less current even if it uses voltage levels as low as the keyboard.


Oh yes it does… 15mA * 3.3V = 49.5mW, but 15mA * 12V = 180mW. Huge difference. Without specifying the voltage, it can be literally anywhere.

By the way, I have read up on it, and basically Bluetooth Low Energy doesn’t support all features, so the tablet antenna is 30mA@3.3V. However, the keyboard part consumes another 10mA so it’s 40mA (130mW) in total. Maybe less.

But now look: these numbers are just for the communication, and the keyboard still needs to function. So it draws extra power from the internal battery. With USB connection, the typical keyboard power consumption is 50mA max (5V), which is 250mW. Let’s add some 250mW for the LED backlight. We get 500mW in total.

But look, we’re not supposed to compare 500mW to 130 mW here. We’re supposed to compare 500mW to 630mW, because the keyboard battery needs recharging afterwards. So yes, Bluetooth is still wasting energy.


Thank you for doing such good research :slight_smile:

So what you’re telling me is that if I unplug my keyboard on the V, it will use ~75% less energy than if it was plugged in. Then once my V dies, and I plug them both in together, they will charge at the same time and the V spending battery to recharge the keyboard won’t matter.


No,that is wrong. It will use MORE energy (630mW vs 500mW), just that it will pull it from the keyboard battery.

You got something wrong here. The keyboard dies before the tablet. So you attach it, it recharges, taking away all the energy it used until now from the main battery, shortening V battery life by the extra 130mW you had been using all the time.


Doesn’t that depend quite strongly on guestimations about the capacity and consumption of the keyboard, coupled with when it is removed from the V?

At worst, I can unplug my keyboard to reduce battery usage if I notice that my V only has 2 hours left, and I can rely on the keyboard lasting at least 2 hours.


I think the keyboard battery lasts for ~18hrs unless the led is on. I think 3hrs is if the led is on constantly.


Actually, it looks like the keyboard uses closer to 1w.

According to this sample, we have roughly a 2.9whr battery.

If the backlight is off, we get ~15hr. But if the backlight is on, only 3.
By my calculation, that’s roughly 200mW with no light and 950mW with backlight (including bluetooth).


That is right, if you only unplug it after V has less than 3 hours left, you’ll save some battery time.

Here I’m talking about backlight enabled, because that’s when it consumes a significant amount of energy. With backlight disabled, it doesn’t really have a noticeable impact on the tablet’s battery life neither wired nor wireless. If you want some numbers, here’s a quick rundown:

For heavy use the tablet’s power consumption can be around 10W, so the battery life without taking into account the keyboard would be 4.8h. If you connect the keyboard in wired mode, with backlight disabled, it will consume around 185W extra, so in total 10.185W -> 4.7h. That’s 6 minutes difference. Now in Bluetooth mode, let’s assume you don’t plug in the keyboard for recharging and take 20mA consumption, a bit lower than the maximum 30mA. That’s 66mW, and 10.066W -> 5.75h. So you win 3 minutes compared to using the keyboard in wired mode, and lose 3 minutes compared to not using the keyboard at all. The results would be pretty much the same for other use scenarios.

@Kirk, that’s some interesting numbers. Seems like I underestimated the backlight, I counted it for 5x 5mm LEDs, which I thought would be sufficient at their peak brightness, but I guess there are way more than that. I forgot the keys aren’t 100% see-through so most light is obstructed. The 200mW part is pretty much in line with my estimate - I just took the maximum probable power consumption, but our keyboard is a bit more efficient than that.


You’re taking the worst numbers and saying that’s the best possible benefit though.

If I like my backlight or am in a dark room and want to see my keys, then removing the 950mW of LED enabled keyboard and replacing it with 66mW connection nets me nearly 10% more life during the “heavy use” cases when at low battery at night. (Basically good for college students in a bind and nobody else)

I admit it isn’t a huge bonus or anything, but this conversation started because someone asked how the Eve power usage was better than something like the Surface Pro. It isn’t the original intent of the keyboard battery, nor is it an all-the-time benefit, but if you consciously use both batteries in an efficient way, there are benefits to be had.


I can’t believe you still don’t get it…
The keyboard’s battery will run out much faster than the tablet’s if you keep backlight enabled. That means you’ll have to recharge it midway, neglecting the whole difference. At first you’ll consume less energy, and it will seem like your battery life is extended, but then your keyboard’s battery will run out, you will plug it in and the charge will go down quick. Returning to even lower than the point where it would have been if you had used the keyboard in wired mode. Because you’ll also have to compensate for the energy you used for Bluetooth.

Nope, neither of these. I’m taking the average numbers (“worst” would be 30mA for tablet’s Bluetooth for example) and saying it’s what you should roughly expect. I’m not taking any biased numbers and I’m not saying it’s the “best” case. Just the average case you should expect.

There is a way to save some battery by using Bluetooth - but you need to disconnect the keyboard from pogo pins only when you have around 2.5h left from your battery. That way you can be almost sure you won’t have to recharge the keyboard. Otherwise, you’re just sucking up the extra power consumption for wireless communication without any benefits.