for anyone who's had their device replaced for this wifi issue you're one of the lucky ones*
bought mine from tesco on 26th, on/off wifi issue began on the night of the same day which can only be fixed by cold starting the device. also, app icons on the home screen randomly stick in their installed location, ie you try and drag one to another preferred area of the screen and it will bounce back to it's first location, this also applies to any widgets and you can't remove them by dragging to the top of the screen, they disappear upwards then reappear exactly where they were so the only option is a factory reset - this is something i've had to do 12 times to date
back to the O/P's topic, yes wifi on during sleep mode does eat battery life compared to having it switch off
now the reason for the *
. i work for tesco, or to be more specific i'm a tech advisor. so it may come as a surprise and maybe a humorous one, that i cannot get my device replaced. why? because the help desk (the one procedure tells me (and you) to contact if there's a technical problem) insist this is a software issue and they wash their hands of all such problems. they referred me to Archos saying i need to re-install the firmware. the problem is Archos website only supports the 97 Carbon under the Elements series dropdown menu. the 80 Cobalt isn't listed and the 80 G9 seems a completely different unit.
so if you've had your device switched for this issue then fair play. the tech advisors probably didn't follow procedure by calling the help desk and replaced your tablet without quibble. this is how it should be and an example of how customer service should behave.
sorry if this seems like a rant, it wasn't
it was meant more of a head's up warning to anyone who bought from tesco a Cobalt 80 that has a 'software' problem, than a disagreement against the policy i have to follow.
edit: as a noob to the android platform i've just discovered Nova Launcher and it's fixed my app icon issues which was my main gripe so i can live with the wifi problem. tbh i don't want to risk replacing a relatively healthy device for one with potential dead pixels even though hardware faults are supposedly covered by our help desk - experience tells me they've more than likely got that covered too by operating under some dead pixel policy clause freeing them from any customer responsibility