2nd NC10 battery I've ordered in a week that is below advertised specification. I hope this is not a common fraudulent activity and is rather a genuine mistake (previous order was from a different seller)
Anyway, the battery has a design capacity of 6600mAh according to windows battery info app and linux /proc/acpi/battery/BAT1/info, this is equivalent to 73.3Wh. The enclosed note says new batteries come discharged but it came partially charged which is a good sign it is a used item, and only 95.5% capacity - so I've only got 6300mAh. EDIT see edit below - after discharge/recharge cycles it gets to 100%
Maybe for £40 that's just about worth it, but you have the inconvenience of a big heavy battery sticking out for only ~1 hour extra usage over the standard 5200mAh battery (which doesn't stick out).
And furthermore, it was missing one of the rubber feet on the bottom, which is a big deal because the netbook now rests at an angle on the battery, so the rubber feet prevent slippage - I had to use one of the rubber feet from the old battery.
I will probably RMA this if it doesn't come up to ~100% capacity after a few recharge cycles.
I was expecting ~8 hours usage from 7800mAh, but if you are happy with ~6 hours usage you get from a bulkier battery then at £40 it's probably ok value
EDIT After two full discharge/recharge cycles (you can discharge the battery using the Battery Calibration utility in the BIOS setup), the battery is reporting 0% wear, ie has full 6600mAh capacity (actually a bit more, 6783mAh or 73260mWh), and on Battery Eater Pro Classic test (intensive cpu and graphics, full screen brightness) it lasts ~6 hours - that is pretty good - since it translates to ~8/9 hours normal use. So maybe the battery is restricted to ~6600mAh to prevent overcharging? In any case, it's not bad value for £40, I upgraded rating from 2 to 3 stars, it would get 5 if it was advertised as 6600mAh
EDIT2 I should have kept this battery. Instead I RMA'ed it and ordered another one from shopping-batteries.co.uk, after nearly 3 weeks it finally arrived, it was also 6600mAh! and a worse shape, it sticks out more than the one here. My advice - you'll struggle to find a true 7800mAh (83Wh) so stick to ~£40 ones like the one here, of if you have the money and only need ~6/7 hours then get the original 5200mAh samsung battery