Don't you have stores in Greece?
Pretty much any electronics store should have batteries, both non-rechargeable AND rechargeable with or without a charger. We have here in all kinds of stores packs of 4-8 AA batteries with a charger starting from about $10.
Anyway... a rechargeable battery goes up to about 1.35-1.38v when fully charged. When completely discharged, it goes down to about 1v
An USB charger, like any cheap mains chargers, use low current to charge the battery, hence why it takes 8-10 hours to charge the battery. But your biggest problem is that those USB chargers don't usually have the intelligence to stop charging, they just send a fixed voltage at a fixed current to the batteries for ever.
For example, this one I see here has fixed voltage at 1.4v:
http://www.amazon.co.uk/TRIXES-Charger-Ni-MH-Rechargeable-Battery/dp/B0058C8YLM/ref=sr_1_8?s=electronics&ie=UTF8&qid=1364322126&sr=1-8If the battery is fully charged at 1.35v it will abuse the battery forever.
Cheap mains charger have some brains in them to detect a voltage threshold and stop, but they don't usually charge at high currents.. here's some good examples:
http://www.amazon.co.uk/Duracell-Battery-Charger-Rechargeable-Batteries/dp/B0038QG674/ref=sr_1_1?s=electronics&ie=UTF8&qid=1364322109&sr=1-1http://www.amazon.co.uk/Energizer-Intelligent-Battery-Charger-AAA/dp/B003ZJ5KDU/ref=sr_1_3?s=electronics&ie=UTF8&qid=1364322109&sr=1-3"Smarter" chargers can pump the batteries with 150-250mA, maybe even more, but this reduces the battery life and also, at such high currents, the batteries have to be cooled down to survive the charging process (these chargers usually have fans or turn themselves off for a period of time when they detect the batteries going over a certain temperature.
If you want the "Rolls Royce" of chargers, you're looking for one of these:
http://www.amazon.co.uk/Technoline-Intelligent-battery-charger-Version/dp/B003S4JQS2/ref=sr_1_8?ie=UTF8&qid=1364321788&sr=8-8http://www.amazon.co.uk/AccuCell-BC-700-intelligent-Battery-Charger/dp/B004X4OZYG/ref=sr_1_20?ie=UTF8&qid=1364321907&sr=8-20http://www.amazon.co.uk/POWEREX-MH-C9000-WIZARDONE-BATTERY-CHARGER/dp/B002BZLMMM/ref=sr_1_18?ie=UTF8&qid=1364321907&sr=8-18http://www.amazon.co.uk/Powerex-MH-C9000-WizardOne-battery-charger/dp/B000OA98SQ/ref=sr_1_5?ie=UTF8&qid=1364321788&sr=8-5Can charge batteries individually, tells you how much charge they hold, can analyze it, discharge it, charge with currents selectable from 0.2 amps to 2amps etc etc
Search for "AA battery charger" if you want to find good results... but eBay is full of crap chinese stuff if you're searching for the cheapest. You're only fooling yourself by buying just the cheapest stuff.