This was supposed to be a winning strategy for battery maker Ener1 (Nasdaq: HEV). Buy a stake in Th!nk Global, supply the electric vehicle maker with batteries, and you make money on both ends of the supply chain. It was a foolproof plan.

Th!nk, which was spun off from Ford (NYSE: F) in 2003, was supposed to be a leader in electric vehicles and was years ahead of the competition. But the plan for EV domination has taken a turn for the worse recently when Th!nk's trouble selling its vehicles worsened. As Nissan, Tesla Motors (Nasdaq: TSLA), General Motors (NYSE: GM), and others have made their way into the electric vehicle space, the tiny vehicles Th!nk made began looking worse to potential buyers.

Inventory of Ener1's batteries built up on the factory floor, and when funding couldn't be lined up to continue operations, Th!nk finally had to call it quits, filing for bankruptcy earlier this week. It's salt in the wound for Ener1 at a time when the company could use some positive news, and it highlights the risks battery makers face right now.

A123 Systems takes charge
With investors uncertain how much business Valence Technology (Nasdaq: VLNC) will lose from Smith Electric's dual-source batteries and Advanced Battery Technologies (Nasdaq: ABAT) under investor scrutiny, A123 Systems (Nasdaq: AONE) looks like the winner of the day. There are still issues, but the company has some of the best partnerships in the industry and enough cash to stay afloat for now.

As for Th!nk, it may be able to rethink its products and emerge from the ashes someday, but Ener1 is left with one of its star customers in bankruptcy. If Ener1 doesn't play its cards right soon, that may be where Ener1 is headed.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.