About three years ago inside a sprawling factory southeast of Pittsburgh, a promising battery startup was churning out some of the first of its ultra-simple, nontoxic, low-cost batteries made from a combination of salt water, carbon and manganese oxide.

With $180 million in funding from some of Silicon Valley’s best-known names, including billionaire Bill Gates, it looked like the batteries could be some of the first with an alternative type of chemistry to provide low-coststoragefor the power grid, buildings, remote machinery and clean energy farms.

But that vision didn't quite pan out. Just a couple of months ago, the battery maker, Aquion Energy, filed for bankruptcy protection, laid off almost all of its workers and ceased selling its stackable energy storage devices. As the company looks for a buyer, it’s also been hit with a lawsuit from former workers who say they were let go without proper notice, and it has been the target of critics who question why the firm was still struggling after receiving state and federal support.

It’s a familiar tale for battery industry watchers. From big companies like A123 Systems, to smaller ones like EnerVault and Imergy, companies developing new types of battery chemistries have faced difficult markets, major technical hurdles, and long sales cycles.

In recent years, however, the dramatically dropping cost of lithium-ion batteries has become chief among the concerns. While some predicted these batteries would become cheaper over time, most didn’t estimate that the prices would go so low so fast -- making the outlook for alternative battery chemistries a lot murkier.

Taking the alternative route

Years ago, alternative-chemistry battery makers pointed to the high cost of lithium-ion batteries as a major differentiator for their novel batteries. But that’s no longer the case as major lithium-ion battery producers like Panasonic, Samsung and LG Chem appear to be selling lithium-ion batteries for less than $300 per kilowatt-hour. In a couple of years' time, lithium-ion batteries could drop below $200 per kilowatt-hour or even $100 per kilowatt-hour.

These low-cost lithium-ion batteries are spawning major growth in electric cars and batteries for buildings and the power grid. But they are wreaking havoc on the businesses of those that placed bets on the other side of lithium-ion price drop.

The situation is similar to the drop in price of silicon-based solar panels that have become much less pricey in recent years; billions of dollars invested in alternative materials for solar panels have been lost over the years alongside the drop in solar panel prices.

So what’s the future for alternative battery makers in the meantime as lithium-ion batteries drive sales and markets?

The model devised by First Solar might provide one answer. First Solar is the rare solar-panel maker that uses an alternative material for its solar panels and has succeeded. The company is now one of the biggest solar-panel makers and solar project developers in the U.S.

Eos Energy Storage, which makes zinc-air batteries, hopes it can be the First Solar of the battery world. The company said it’s already selling its batteries for $160 per kilowatt-hour and has done a handful of pilots with big utilities like Con Ed and Engie. The company has pledged eventually to sell batteries for under $100 per kilowatt-hour.

“We're one of, if not the only, technology that has structural cost entitlement advantage over lithium-ion,” said Eos Energy Storage’s CEO and co-founder Michael Oster. “At $160 per kilowatt-hour today, we’re 30 percent to 40 percent less expensive on an apples-to-apples basis.”

The company is also literally taking cues from the First Solar playbook. At the end of 2016, Eos Energy Storage brought on Jim Hughes, the former CEO of First Solar, as chairman of the board.

Striving to be the low-cost winner

Other alternative-chemistry battery makers agree that cost is king when it comes to competing with lithium-ion batteries. It’s not so much about new or alternative applications anymore, but rather sheer cost per kilowatt-hour.

Ambri, a Cambridge, Massachusetts-based company which makes a liquid metal battery, has faced some delays getting its battery to market after opting to redesign the battery’s seals. But when Ambri does start shipping batteries, company leaders have pledged its prices will be low.

Ambri’s CEO Phil Giudice said, “Our offering continues to be distinguished even in the face of lithium-ion prices.” The company hasn’t disclosed its battery prices over the years.

Ambri aims to continue working on its battery in 2017 and early 2018. After that, it hopes to start shipping batteries to its list of demonstration partners in the second half of 2018.

Another alternative-chemistry battery maker, Fluidic Energy, based in Scottsdale, Arizona, has already shipped 100,000 of its zinc-air batteries to customers around the world. It’s also raised $200 million to do so.

The company said cracking the code to making a zinc battery rechargeable is the key. Fluidic Energy’s CEO Steve Scharnhorst told Fortune that “fundamentally zinc is the lowest-cost winner for energy storage.” Many of its current customers are telcos in developing countries that have off-grid networks.

But these companies’ customer lists are relatively small, compared to the big battery behemoths of the world. It doesn’t help the alternative-chemistry battery makers that huge companies like Samsung, LG Chem and Panasonic have big balance sheets that can enable them to sell batteries for slim (or even zero) margins if need be.

And then there’s Elon Musk and Tesla, which are building a massive Gigafactory outside of Reno, Nevada in order to churn out low-cost lithium-ion batteries for Tesla cars, the power grid and buildings. Musk tends to have the ability not only to predict markets, but sometimes also to move them.

While lithium-ion batteries will likely reign supreme for years to come, eventually some kind of chemistry will emerge that will be safer to use and potentially lower-cost. Will today’s alternative battery startups be able to hold on long enough to get them there?