You quote this for use for those living in isolated areas, well have you thought about those who actually live in remote areas, and how difficult it is for them to recharge their card.
To save a penny to the big power suppliers at the expense of the little guy is not a practical system.
What happens is the user can not get to town due to bad weather conditions, car problems, etc. for a recharge and the credit expires, the loss of power to basic needs could be life threatening, not to mention things like spoilt food from no fridge, loss of water.....etc,etc.
Sorry i dont agree with the cost cutting and the loss of jobs for basic people so the big can get richer.
I will not help you to program your eeprom for those reasons.
Pete.