You are treating a symptom and not a cause.
If you are using up batteries there's something wrong with the charging system.The workshop manual has checks for the Stator and the Regulator/Rectifier.
In a previous post I pointed to these Power Boost Jump Starters,
https://www.amazon.co.uk/DBPOWER-800...r+jump+starter
I have a pal who has one and they work.