Laptop starts then every 5 min goes in sleep

Hi all got cq61 and had thread up about screen blank well got it fixed in shop it was connecter on motherboard and lcd cable . well wen i start it it comes on then after 5 min it goes like into sleep screen goes off but i can faintly see in background i cant press anything to get it back on but i close the lid reopen it and most of time it sound like it gone off but the on off light flashes on/off constant then i press touch pad and on it comes . as normal then 5 min and same thing , but then just now it went off completely .. now i checked all sleep and hibernation setting turned them all to never.. also i know battery is faulty as even when fully charged laptop goes off .. what could be problem please help

hi all took it back to shop and they saying its definate the battery they say £60 for new battery i know could prob get it cheaper can anyone reccomend where as i know off ebay would prob be sodgy remake or something ? also does the MaH matter like the origanal battery is 10.8v and 4200mah i see battery on ebay 10.8v and 4400 mah and 5200 mah does this matter thanks in advance