Think B.I.G. Hawaiʻi← ToolboxCompare lithium (LFP and NMC), lead-acid, nickel-iron and the new sodium-ion batteries side by side. See how each one works, what it really costs over 20 years, and how to avoid a bad unit. Figures come from U.S. Department of Energy labs, independent tester Will Prowse, and manufacturer data, with every source linked. Prices checked November 2026.
Your answer tailors the recommendation and the cost calculator below.
Panels from established makers are now largely interchangeable, and they are very good. NREL's review of about 2,000 field measurements found panels lose a median of just 0.5% of their output a year S8. A newer NREL-led test of 834 modules from 7 manufacturers in 3 climates measured a median of 0.58% a year, in line with older panels S9. U.S. module prices sat near 28 to 30 cents a watt through mid-2026 S10.
There's still a long tail of poorer products, which pulls NREL's average loss up to 0.8% a year S8. Buy from an established maker, check for a UL 61730 listing, and then shop on price.
A battery is a sealed box of cells, wires and a battery management system (BMS). You can't see what's inside, and makers of uncertified batteries can change the cells or BMS whenever they want. Will Prowse warns that what he reviews may not be what you receive S2.
In June 2026 Prowse found that Wattcycle batteries bought by ordinary customers had regular cables in place of braided ones, no thick metal busbars, and a mix of different cells, unlike the unit the maker had sent him to review S5. Price is no guarantee either. His 2026 teardowns of premium-priced Battle Born batteries found BMS disconnects, overheating and melted parts S6. Battle Born had ended his affiliate account months earlier, which some readers weigh as context S7.
Pick one to see how it stores energy and how it scores. The bars use the conservative figures from the calculator below. Yellow marks figures we couldn't confirm from an independent source.
Scores of 1 to 5 are Think B.I.G.'s summary of the figures on this page, not a lab rating. The dashed outline is LFP for comparison.
Both are lithium-ion. LFP (lithium iron phosphate) has no nickel or cobalt. DOE's lab assessment gives it about 2,400 full cycles at 80% depth and a 16-year life, against 1,520 cycles and 13 years for nickel-based NMC S12. LFP packs were also cheaper in 2025, averaging $81/kWh worldwide against $128 for NMC S14.
Safety varies cell to cell, but DNV's testing shows thermal-runaway temperatures differ widely between chemistries and even between LFP products S34. That's another reason to insist on a UL 9540A fire test. Tesla's Powerwall 2, an earlier nickel-based design, was recalled in November 2025 after 22 overheating reports S32.
Most new home batteries, including the Powerwall 3, Enphase IQ 5P and the DIY wall units below, are LFP.
The cheapest battery to buy is often the most expensive to own. This calculator sizes a bank for your need, then counts replacements, shipping to the islands and energy lost to inefficiency over the years you choose.
Striped bars use estimated prices or an emerging chemistry. Lower is better.
Each jump is a replacement bank. Totals aren't discounted for inflation or interest.
Cycle life is counted in full equivalent cycles at the rated depth of discharge. A bank sized for two days but drained one day's worth each night uses half a cycle a night. Life is whichever runs out first, cycles or calendar years. "Usable" is the share of nameplate capacity you can draw routinely without shortening life: about half for lead-acid, per Trojan S26.
Most of this comes from Will Prowse, who load-tests, cycle-tests and abuses the batteries he recommends and drops any that fail S1.
Server racks stack: three 5.12 kWh units make a 15 kWh bank, and you can add more later. Buying locally skips hazardous-cargo freight, but a Marketplace battery has no seller warranty and an unknown history. Capacity-test it before you pay, check that the model is UL-listed if you'll get a permit, and ask for the original invoice and the cells' manufacture date.
Other DIY prices are mainland list prices before freight. Installed prices include labor and the inverter, so they aren't comparable with battery-only prices.
Battery packs hit a record low average of $108/kWh worldwide in 2025, and packs for stationary storage fell 45% to $70/kWh S14. In 2026 that trend paused. Lithium carbonate climbed back to about ¥150,000 a tonne, and China is cutting its export tax rebate on batteries from 9% to 6% in 2026 and to zero from January 2027 S16.
U.S. tariffs add more. The Section 301 duty on Chinese non-EV lithium-ion batteries rose from 7.5% to 25% on January 1, 2026 S17, while separate emergency (IEEPA) tariffs were struck down by the courts earlier this year S18.
Homeowners who buy: no federal credit. The 30% Residential Clean Energy Credit (25D) covered home batteries as well as solar, and it ended for both after December 31, 2025 S19 S43.
Businesses, nonprofits and leased home systems: batteries still get the 30% §48E credit. Unlike solar and wind, storage keeps it for projects that start construction through 2033, phasing out after that S44. Leased or PPA home batteries qualify through the company that owns them S20. Nonprofits and local governments can take it as a cash payment through elective (direct) pay S45. The catch: from 2026, batteries with too much content from "foreign entities of concern," mainly Chinese suppliers, lose the credit entirely S46. Many budget imports won't qualify, so get the maker's FEOC certification in writing and talk to a tax adviser.
Business solar keeps the credit only if construction began by July 4, 2026, or the system is in service by the end of 2027 S45.
Hawaiian Electric's BYOD Plus pays $400 per kW you commit to export for a 2-hour evening window, with no cap, plus another $400/kW for low-to-moderate-income customers S21. Committing 5 kW earns $2,000 up front. It requires a 5-year commitment and solar charging, and businesses can join too S39.
Lead-acid isn't obsolete for every job. A PNNL storage researcher notes that in backup power and off-grid systems, lead-acid offers proven reliability, a mature supply and service network, and well-understood safety and recycling S35. For a battery that sits full and rarely cycles, its low upfront price can win; try "Backup" in the calculator. It loses on frequent deep cycling, where DOE expects it to last only 3 to 4 years at one cycle a day S12.
Nickel-iron appeals to people who want a battery that may outlast them. Iron Edison rates its cells for 11,000 cycles at 80% depth and a 30-year float life S29. The catch is energy: research puts its round-trip efficiency at 50% to 80% and self-discharge at 1% to 2% a day S30, so you need a bigger solar array to fill it, and it's very heavy.
Sodium-ion uses no lithium, cobalt or nickel. UNIGRID's first home battery is rated for 10,000 full cycles and is due in the U.S. by the end of 2026; Biwatt and Lithium Valley already hold UL certifications for the U.S. market S31. Those ratings are new and untested in the field, so we treat it as one to watch.