SOLVED !!!!!!!
After trying everything like , PRAM reset , SMC reset and removed many apps, tried whole lot of things which i found over internet. even took my Mac Air, to the authorised service centre and advised to replace battery which cost around 180$. i decided to do some trials, something i do to my android & windows device. and for android and windows PC the most workable option always is to Factory Reset the device. i decided to give this a shot and reset my mac to its factory settings, like completely new, everything is formatted. and it did work for me. i even downgreded to Maverics considering the problem with EL Capitan. but Service battery notification remined as it is, as well not good interface and appearance compared to El Capitan. so problem is not with El capitan. i think the problem appears when you upgrade from yosemite to El capitan.
what i got after factory reset :
1) battery not as good as new but still better than before, get around 8 hours of backup now. (before reset getting 3 hours)
2) heating problem solved. no more heating.
3) performance incresed, exactly as new.
4) Service battery notifcation disappeared.
How to factory reset :
1) first backup everything to external hdd.
2) and follow the process as shown in video - https://www.youtube.com/watch?v=FHwclR_QLcc
3) You don't need any bootable CD.
4) you will need active internet connection
5) will take more than 8 hours for 1mbps internet speed.
6) there is different process if you have made a Boot camp partition, be careful.
Few Things to be considered after reseting your mac :
(this instructions are considering old macbook airs, and for those who don't want to invest 200$ right away)
1) Do not install Chrome browser— i am not saying this is exactly the issue. but there are lot of post regarding performance of mac with this browser. i am using Safari, and its good too, i am very much familiar with Chrome but still its better to use Safari for 8 hours than Chrome for 2 hours.
2) Do not install unnecessary apps — while experimenting performance by deleting one by one app i realised there too many apps i had installed which i don't really use. and most of them unncesry take space as well CPU in aground.
3) Avoid installing Pirated Apps — lot of apps which come through torrent come with patch or crack, most of them contains viruses. and they usually run in aground and use your network and CPU. if you use high end softwares and you can't afford to buy, simply be aware before downloading... look for other users comments and avoid downloading if even single user mentioned that there is virus/malware.
4) Use Apple APP STORE for apps — most of needed apps are available in appa store. so rather than downing apps directly from software official webpage, download it from Apple store. as each app has to go through apples criteria. you don't have to worry about this apps.
5) Avoid using Parallel Desktop or other VM — you can install it but make sure you really need it. i realised i unnecessarily kept it on my mac. which was consuming mms disk space. which almost of half my entire capacity ( 128gb is my HDD)
6) Do not install MAC Cleaners/anti viruses— simply not needed and it has very bad effects on your mac.
7) Do not add too many internet accounts — i had kept so many accounts, like 2 Google accounts, one Facebook, twitter, office mails, etc. and most of them synced for many features like, calendars, mails, notes. this put effect on performance, so many accounts always synching. Sync only accounts which you really use.
8) try to manage your Files — keep organised all the files. try to shift bulky data to external HDD, data like, Musics, videos,movies, app installers. they consume lot of space. e.g.. when we download music and add to playlist, it gets copied into iTunes folder. so we have 2 copies of on our mac. so try to move the original to HDD or simply delete it.
9) Restart/shut down mac once a week — don't just keep working on your mac for months without restarting it. it can not clear some cache memory ( i guess) and it keeps on building temporary memory . as well it is unable to reset individual apps.
It took a lot of time to write the above thing, but this is what solved my problem. i was searching for solution for very long and i don't want anyone to face this problem anymore. if anyone having any issue regarding this reply to this post, i will try to get back. thanks.
