Hello SandiMahendra,
Thank you for using Apple Support Communities! I understand from the information you provided that the Mail app is draining your battery; I'd like to help.
Keep in mind the screenshoot you provided is showing which apps used the most battery over the last 24 hours. If it's been less than 24 hours since you deleted the Mail app, it will still show here, even if you recently deleted it.
The sync or fetch settings you have enabled in Mail can contribute to its battery usage. You may need to adjust how often the Mail app is checking for new mail messages. The following support article provides some information about how to adjust these settings:
If you can't receive email on your iPhone, iPad, or iPod touch - Apple Support
This article also explains more about the battery and its performance in the iPhone. This can help you to check the overall health of your battery:
iPhone Battery and Performance - Apple Support
Hope this helps.
Best Regards.