hiya
It's the internal battery that's fading probably. You usually hear of this on desktop computers, but I'm pretty sure laptops have them as well. Pretty rare occurence in laptops really, but it's the first thing that pops to mind.
fixable? yes, costs and faffing about doing the fix? could be quite cheap to expensive depending on how much faffing about opening everything up to get to the battery is!
have a look on the manufacturers website and see if theres a diagram for which you could follow and possibly do yourself. it's unlikely though, as it's probably on the motherboard somewhere but you might get lucky.
Have a search on forums to see if this model is prone to this kind of issue and any recomendations on where/costs to fix it. The battery itself will be 2 quid/bux - the labour charge to install it will be the bulk of the cost to fix
Cheers, DtM! West London & Slough UK!