How a solar battery works and how to choose the right size for your home

Solar panels generate power during daylight hours, with output varying by sun angle, cloud cover and season. Your electricity bill drops. Life is good, until the grid goes down at 8 pm and none of that daytime generation is available to you. Net metering credits are real and useful, but they don't keep the fans running during a power cut in Nagpur in June. A solar battery solves that problem by storing what your panels produce during the day and making it available whenever you actually need it. A home solar backup battery is, in short, what turns a grid-tied system into one that genuinely works for you around the clock.

At Bearworx, we've completed battery-backed rooftop projects for hundreds of homeowners and businesses across India, ranging from small 3 kW residential systems to large-scale BESS installations. The two questions we hear at every site visit are the same: "Which battery type should I buy?" and "What size do I actually need?" This guide answers both, with actual numbers you can use.

What a solar battery actually does and why Indian homes need one

A solar storage battery sits between your solar array and your home's electrical loads. During the day, your panels produce DC electricity. A hybrid inverter or charge controller manages how much of that energy goes directly to your home, how much charges the battery, and how much exports to the grid. When the grid fails or the sun sets, the battery discharges and the inverter converts stored DC back to AC for your appliances.

Under the PM Surya Ghar scheme, many homes now have 3 kW systems producing surplus power on sunny afternoons. Without storage, that surplus exports to the DISCOM for a net metering credit. With a solar battery, that same energy stays in your home and powers your evening loads. The credit is useful; having actual electricity during an outage is more useful.

For commercial and industrial users, the calculation looks different. A business with a 50 kW solar plant can use a Battery Energy Storage System to discharge during evening peak tariff hours, potentially reducing demand charges on their monthly bill, in some modelled scenarios by 30–35%, depending on tariff structure and load profile. Both residential backup and commercial peak-shaving are valid applications, but the sizing logic differs, as you'll see below.

How PV energy moves into and out of a battery

Solar panels produce DC, which flows through a charge controller or hybrid inverter. The Battery Management System (BMS) inside the battery monitors cell voltage, temperature and current to protect the cells during charging. When you draw power, the process reverses: the BMS manages discharge, and the inverter converts DC back to AC. Battery voltage (12 V, 24 V or 48 V) determines system architecture. A 48 V system at the same kWh capacity carries lower current through the cables, which means less heat and better efficiency.

Where solar batteries fit under PM Surya Ghar and net metering

PM Surya Ghar provides a central subsidy of up to ₹78,000 for a 3 kW or larger rooftop solar system. Importantly, the subsidy is calculated on the solar module capacity only. A battery is a privately financed add-on; there is no separate central subsidy for storage. That said, the battery is what makes your solar investment work around the clock, and in states like Rajasthan, Maharashtra and Gujarat, battery-coupled systems remain eligible for net metering provided the inverter is grid-synchronised and anti-islanding compliant. For the latest subsidy figures and eligibility conditions, refer to the official PM Surya Ghar scheme documentation or consult your installer.

The three main battery chemistries compared

Indian buyers encounter three real options: flooded/tubular lead-acid, conventional lithium-ion (NMC), and lithium iron phosphate (LFP/LiFePO4). Each has a different cost profile, lifespan and maintenance requirement. Here is how they compare.

Lead-acid and tubular batteries: the familiar starting point

Lead-acid batteries, particularly tubular and VRLA/AGM types from brands like Exide, Amaron and Luminous, are what most Indian homes have used for decades. A 150 Ah, 12 V tubular battery costs ₹12,000–₹20,000 upfront, which looks attractive. The catch is that you can only use about 50% of that capacity regularly without damaging the cells, giving you roughly 0.9 kWh of usable energy. Cycle life is 500–1,500 cycles, service life is 3–5 years, and heat shortens that further. For occasional backup in a mild climate, a lead-acid solar battery works. For daily cycling in a hot Indian climate, it is an expensive long-term choice. If you are evaluating a deep-cycle battery for solar use, lead-acid is the entry-level option, but the lifetime costs deserve scrutiny before you commit.

Lithium iron phosphate (LFP): the better long-term bet

LFP batteries offer 80–90% usable depth of discharge, 3,000–6,000 cycles, and 8–12 years of service life. Thermal stability is considerably better than NMC chemistry, LFP cells typically remain stable at operating temperatures well above 45°C, which matters in Indian summers, whereas NMC cells are more sensitive to high ambient conditions and require robust thermal management. Brands like Pylontech, Livguard, Luminous, Waaree and Exide's LiFE range now offer LFP systems for Indian homes. A 1.28 kWh LFP pack (100 Ah at 12.8 V) starts at ₹27,000–₹40,000, higher upfront than lead-acid, but the cost per cycle over the battery's life is lower. For a home that cycles its solar battery every day, LFP is the clear choice.

Cycle life and warranty: reading the fine print

A "5,000 cycle" claim is only meaningful if the manufacturer states the depth of discharge, ambient temperature and end-of-life capacity at which that rating applies. Always ask for the guaranteed remaining capacity at the end of the warranty period. A quality LFP warranty specifies 70–80% retained capacity. Lead-acid warranties typically run 24–36 months; quality LFP warranties range from 5 to 10 years. If a seller cannot produce those numbers in writing, treat the warranty claim with scepticism.

How to calculate the right solar battery size for your home

Sizing a battery correctly requires three steps: list the appliances that must run during a power cut, apply the sizing formula, then sanity-check against a BHK reference range. Do them in order.

Step 1: List only the appliances that need to run during a power cut

Focus on essentials only. Typical backup loads include LED bulbs (7–12 W each), ceiling fans (50–75 W), a Wi-Fi router (10–15 W), a television (80–150 W) and a refrigerator averaged over its compressor cycle (80–150 W). A typical Indian home running lights, fans, a fridge and a TV draws 300–700 W without an air conditioner. Air conditioners require a substantially larger system and should be planned separately, not added as an afterthought.

Step 2: Apply the sizing formula with a worked example

The formula is: Battery kWh = (Load W × Backup hours) ÷ (1,000 × DoD × inverter efficiency) × ageing margin. Here is what that looks like with real numbers. A typical 3 BHK essential load: 3 ceiling fans (180 W) + 6 LED lights (60 W) + router (15 W) + TV (100 W) + fridge (120 W) + chargers (20 W) = 495 W total. For 8 hours of backup: (495 × 8) ÷ (1,000 × 0.9 × 0.9) × 1.2 = approximately 5.9 kWh. The practical choice is a 6–7.5 kWh LFP battery, or at 48 V, a 150 Ah bank.

As a reference check, use these BHK starting ranges for 4–6 hours of essential backup (no AC):

• 1 BHK: 2–3 kWh LFP

• 2 BHK: 3–5 kWh LFP

• 3 BHK: 5–8 kWh LFP

These ranges are starting points, not substitutes for an appliance-by-appliance calculation. Site conditions, usage habits and appliance efficiency all affect the final number.

Step 3: Convert kWh to Ah based on system voltage

Ah figures are meaningless without voltage. The formula is: Battery Ah = (kWh × 1,000) ÷ Voltage. A 48 V, 150 Ah battery gives 7.2 kWh nominal. A 12 V, 150 Ah battery gives 1.8 kWh nominal. These are not comparable, and buyers who shop by Ah alone routinely undersize or overpay for their systems. Always compare kWh, not Ah, when evaluating different solar battery products.

What a solar battery costs in India in 2026

The right metric for comparing batteries is cost per usable kWh, not cost per Ah, a distinction that becomes clear once you account for depth of discharge differences between chemistries. Here is where the market stands in 2026, based on current retail and installer pricing.

Lead-acid pricing: low entry cost, hidden long-term cost

Tubular lead-acid batteries start at ₹12,000–₹20,000 for 150 Ah at 12 V, which is roughly 1.8 kWh nominal and about 0.9 kWh usable. That puts usable cost at ₹13,000–₹22,000 per usable kWh. Factor in a 3–5 year replacement cycle against 8–12 years for LFP, and the lifetime cost of lead-acid is not as low as the sticker suggests.

LFP pricing and why cost per kWh is the right metric

LFP packs in India currently range from ₹27,000–₹40,000 for a 1.28 kWh pack (100 Ah at 12.8 V) to ₹1,90,000–₹2,30,000 for a 10.24 kWh pack (200 Ah at 51.2 V). Larger packs offer a lower per-kWh price: small 12 V packs cost roughly ₹21,000–₹31,000/kWh, while 51.2 V packs drop to ₹18,500–₹22,500/kWh. For a complete 5 kWh home solar battery system including a compatible hybrid inverter, DC cabling, protection, installation and GST, expect ₹1,50,000–₹2,50,000 installed, depending on inverter brand and site complexity. These figures reflect 2026 market conditions and will vary by brand and configuration.

The payback period for adding a 5 kWh LFP battery to a 3 kW rooftop system is typically 7–9 years under normal grid conditions, assuming current retail tariffs and daily cycling. In areas with frequent outages or where the battery displaces diesel generator costs, that drops to 4–6 years. Given an expected 10–12 year service life, the financial case is sound in high-outage regions and tighter in areas with reliable grid supply.

Compatibility essentials before you connect anything

Buying the wrong battery for your inverter is an expensive mistake, one that can create financial loss, safety risks, or both. There are three checks that protect you from it.

Matching battery voltage to your inverter and charge controller

The battery bank voltage (12 V, 24 V or 48 V) must be supported by both the inverter and the charge controller. This also applies when selecting a solar inverter battery combination: confirm that the inverter's charge profile is explicitly compatible with the battery's chemistry, not just its nominal voltage. Nominal voltage alone is not sufficient, compare the battery's full-charge voltage against the inverter's DC input range. For example, a 51.2 V nominal LFP battery (often marketed as "48 V") may charge up to approximately 58.4 V; always check the specific product datasheet for the full-charge voltage and confirm your inverter handles that ceiling. Many older inverters do not.

BMS communication: the step most buyers skip

Lithium batteries communicate with hybrid inverters via CAN bus or RS-485. Without a confirmed, working communication link, the inverter falls back to fixed charge settings. This disables the BMS's dynamic protections and can silently damage the battery or trigger safety shutdowns. Before purchasing, confirm the exact protocol, firmware version, cable pinout and whether the inverter has the battery profile loaded. "Both have a CAN port" is not sufficient confirmation.

Surge current and what it means for motor loads

A 5 kW inverter on a 48 V system draws over 100 A at full load. When a refrigerator compressor or pump starts, the startup current spikes well beyond that. The battery's BMS must support the peak discharge current for the duration of the surge. If it cannot, the BMS trips, the inverter shuts down, and your essential loads go dark. Always verify peak surge ratings, not just continuous discharge ratings, before commissioning.

Choosing the right solar battery for your home

The compatibility checks above apply regardless of which chemistry you select. Whether you are evaluating an LFP pack, a deep-cycle battery for solar backup, or a solar inverter battery bundle offered by a single supplier, run all three checks before signing off on any purchase order. Getting this right at the selection stage costs nothing; getting it wrong after installation costs significantly more.

How Bearworx designs and installs solar battery systems

Every battery project at Bearworx starts with a site assessment, not a quotation. We map the appliance load, evaluate the existing solar capacity, check the inverter model against the shortlisted battery's BMS protocol, and design the bank to actual usable requirements. This process prevents the sizing and compatibility mistakes that end up as warranty disputes or repeat visits.

As representative examples of completed projects: a homeowner in Rajasthan with a 3 kW PM Surya Ghar rooftop added a 5.12 kWh LFP solar battery system through Bearworx, with evening grid draw falling to near zero. A commercial client with a 50 kW solar plant worked with Bearworx to design a BESS for peak demand shifting, with modelled bill savings in the range of 30–35% depending on tariff and load conditions. Both projects were designed, installed and commissioned under a single Bearworx contract, covering everything from string layout and DC cabling to inverter configuration and commissioning tests.

Post-installation, Bearworx offers performance monitoring, scheduled preventive maintenance and on-site support through its AMC plans, with financing options available for both residential and commercial customers. If you are ready to size your system properly, get in touch with our team for a no-obligation site assessment.

The decision framework, in plain terms

Start with your load. List the appliances that must run during an outage, multiply by your required backup hours, and apply the sizing formula. Use the BHK reference ranges only as a sanity check. Size in kWh, not Ah, and convert to Ah only after you have fixed your system voltage.

Choose LFP for any system that will cycle daily. Lead-acid remains viable for occasional backup on a tight upfront budget, but factor in the replacement cost before deciding it is cheaper. Verify inverter voltage compatibility, BMS communication protocol and surge current ratings before purchase. Read the warranty document, not just the headline period: the guaranteed end-of-life capacity and operating conditions are what the warranty is actually worth.

If you would rather skip the guesswork entirely, reach out to Bearworx for a site assessment. We will size the solar battery, handle procurement, install it correctly and monitor it after commissioning, so the only thing you need to manage is how you spend the money you save on electricity.