I recently purchased a Portege ct 7000 lap-top for college used for about $100. it works great in al respects other than the battery. When I recharged it it would onlytake a 30% charge and and after repeated recharging this is degrading. I have priced batteries on several websites and most cost more than what I paid for the whole kit. I have found several off brand batteries for non-Ct series portege 7000 models that look almost identical to mine. Will these work or do I need a CT series battery?