What about the case of Aries M. DeGeus, he was working on a long lasting battery and was found dead in his car in the airport carpark on his way to get funding for his research.
What about the thousands of other researchers who are working on much better batteries and who aren't dead? Are the Secret Conspirators too busy partying with the aliens to have noticed them?
I'm not surprised that a few scientists and engineers working have in energy-related areas have died suddenly. I'm not even surprised that a handful have been murdered. There are many scientists and engineers working in energy-related areas. It's not surprising that a few will have heart attacks or strokes and one or two will be murdered - that would be true for any similarly large number of people.
The underlying problem with your conspiracy story is that, as has been pointed out already, it makes no sense. Even if there was a capitalist conspiracy so secret and so powerful that it could kill people at will without any fear of the consequences, there's no motive.
Let's say that I somehow uncover something that enables me to make a battery that has a charge to weight ratio 20 times as high as Li-ion, which doesn't use any rare materials, which has very little environmental impact during manufacturing, which is recyclable and which can go through many charge/discharge cycles with very little loss of maximum charge.
I could print a list of major companies, regardless of what business they are in, close my eyes, spin round, poke a finger at the list at random and be guaranteed to find a company that would pay huge sums of money for my invention because they'd make even more money from being the first to market with it. Companies aren't pouring billions into battery research because they're bored and need to get rid of the money somehow.
With electricity generation, I could accept the possibility of a political conspiracy if there was any evidence for one, since a really radical new method would have global political effects. But a capitalist conspiracy is obvious nonsense - they'd profit from it, not murder to suppress it. There's no evidence and it makes no sense - it's not in the slightest bit plausible.