Australian taxpayers will have to bear a burden of up to $150 million in costs to provide millions of phone subscribers to National Broadband Network (NBN) with back-up batteries.

As per estimates, as many as 11 million phone subscribers to NBN will require back-up batteries to make emergency calls during a power outage.

The McKinsey-KPMG implementation study into the NBN claims that around 2-4 million back-up batteries will be disposed of annually, putting an additional burden of $90-$150 million per year on the taxpayer.

Describing the costs, the implementation study stated, "This estimate is based on a high-quality sealed lead acid battery, which costs approximately $40 and has an operational life of three to five years."

The costs were estimated based on discounted wholesale rates for lead batteries of between 66-79 per cent. It may also be noted here that the implementation study's $43 billion costing of the NBN didn't include the cost of a power-supply unit to house the batteries.

In addition, the study recommended that back-up batteries should not be made mandatory as it would trigger the environmental hazards of battery disposal.

Overall, taxpayers will have to pay for around $26 billion of the total spending for the intended high-speed broadband project, NBN.