Hi, I stumbled upon your message from google. I have in fact recently released an android app called 'Skana Battery Alerts'. It shows smart, highly customisable alerts on high battery, low battery or when charge cable is removed. I swear on my life that you would have not seen a more customisable battery alerts app. It is based on a new UI/UX scheme called D-Follow which aims to make each part of the app highly responsive according to user behavior. You can experience D-Follow at (youtube) : goo(.)gl/lwWyTR
You can get the free version of the app at (fit for your use case):
goo(.)gl/8jQiqg
If you want the paid version you can visit :
goo(.)gl/fOq2hE
Now, remember one thing the reason that most battery alert apps don't provide low battery alarms because constantly querying the phone for battery level is a costly affair. But, Skana Battery Alerts app uses a smart predictive algorithm to assess a reasonable launch time at least possible resource usage. The trade-off is that your low battery alers (only) might be off by a level or two. Be sure it saves tons of your battery.
I hope you like the app. Contact me at : skanaworks(at)gmail.com