I gave this 2008 Macbook 5,1 to my son and he keeps forgetting his charger at school. He has been charging it on his Mom's 2011 MacBook Pro mag safe charger each night - a 60W A1344. Is there any big difference in the chargers? Have we damaged the battery? It seems to only hold a charge for 20 minutes vs about 4 hours before. The battery has about 448 cycles.