Most storage conversations stop at capex. Someone quotes a number per kWh, the buyer compares two quotes, and the decision gets made. But a battery is a fifteen-year asset, and what it costs to run determines whether the payback in the spreadsheet survives contact with reality.
The good news is that running a battery is genuinely cheap compared with the alternatives. The catch is that “cheap” is not “free”, and the costs that bite are rarely the ones on the maintenance invoice.
The headline number
The widely used benchmark for utility-scale battery storage is that annual operations and maintenance costs run at roughly 2% of capital cost per year — often expressed as around USD 2.5 per kWh per year. Other estimates for commercial and utility projects put the range slightly wider, at about 2 to 2.5% of initial capex.
That covers the routine work: preventive maintenance visits, remote monitoring, spares, and response when something faults.
A word of caution before you build a model on it. Published India-specific O&M data is much thinner than India-specific capex data, and a good deal of what circulates online is vendor estimate rather than audited operating experience. Use these percentages as a sanity check on a bid, not as a substitute for a firm quoted scope.
The four buckets that make up OPEX
Treating “O&M” as one number is where budgets go wrong. Operating expenditure on a storage project really sits in four distinct places.
1. The O&M service contract. Preventive maintenance, remote monitoring, emergency response. This is the invoice most people picture.
2. Insurance. Storage is underwritten as its own risk class, priced on chemistry, fire protection and siting. It is a real annual cost and it has been getting firmer, not softer — we cover this in detail in our guide to insuring a BESS in India.
3. Grid connection and wheeling charges, plus auxiliary power. Auxiliary load is the quiet one. A battery consumes electricity to run its own thermal management, controls and power conversion. You do not get an invoice for it; you get less usable output than the nameplate suggests. That is the same round-trip efficiency question we unpack in our article on round-trip efficiency and degradation.
4. Warranty and degradation guarantee premiums. Holding a supplier to a capacity number for a decade costs something, and it is priced in somewhere — either as an explicit premium or inside a higher capex.
The cost that is not in any of those buckets
Cells fade. A system that delivers its rated energy on day one delivers less in year seven, and if your contract obliges you to supply a fixed quantity every evening, someone has to make up the difference.
That is augmentation — adding capacity mid-life to hold usable energy flat. It is not routine maintenance and it does not belong in an annual O&M percentage. It is a planned capital event, and on a fifteen-year contract it is often the single largest post-construction spend. Our augmentation explainer walks through how operators plan and price it, and our warranty guide covers what a degradation guarantee should actually promise.
| Cost item | Rough shape | Shows up as |
|---|---|---|
| O&M service contract | ~2–2.5% of capex per year | Annual invoice |
| Insurance | Priced on chemistry and fire protection | Annual premium |
| Auxiliary load | A few percent of throughput | Reduced usable output |
| Grid / wheeling charges | Tariff and state dependent | Utility bill |
| Augmentation | Lumpy, mid-life | Capital event |
What this means for you
- If you are a C&I buyer: ask every bidder to quote O&M as a separate, scoped, multi-year line rather than folding it into a headline price. Then ask what happens in year eight when usable capacity has dropped — the answer tells you whether you are buying a system or a relationship.
- If you are a developer or IPP: model augmentation explicitly with a date and a number. A project that pencils on capex alone and ignores mid-life top-up is not a project, it is an optimistic spreadsheet.
- If you are comparing against diesel: running cost is where storage wins decisively, because there is no fuel bill. Our BESS versus diesel genset comparison sets out that arithmetic, and our standalone storage solutions page shows the configurations these numbers apply to.
The benchmarks above are drawn from international published sources and industry estimates, and real O&M pricing varies widely with site conditions, chemistry, contract scope and how hard the system is cycled. Treat them as a starting sanity check rather than a quotation. To model running costs against your own tariff and load profile, try our BESS savings calculator, or get in touch with our team.