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.