My blade on my 21" mower got dinged up pretty bad so I bought a replacement universal blade. It was 20" so I figured it would be ok. When I first used it it appeared the battery did not last as long. Do you HAVE to use an EGO replacement blade? I only cut my front. I am going to see if I can finish the rear on a full charge. I know fully charged I have completed the back yard before. Any ideas????