In a filing with the SEC, Berkshire revealed it held 2.3 million shares as of June 30.
The stake is worth about $361 million, indicating the decision to buy was almost certainly made by one of Berkshire's portfolio managers, not by Buffett himself.
Charter provides broadband communications and said it is the fourth-largest cable operator in the U.S.
The filing also showed Berkshire made some substantial additions to stakes it already held.
The company's holdings of IBM, a stock that Buffett did buy for Berkshire's portfolio, increased by 3 percent to 70.2 million shares. At Thursday's closing price, the additional stock has a market value of $341.5 million. The entire stake is valued at $13.2 billion.
Berkshire boosted its holdings of Verizon Communications by 36 percent to a little more than 15 million shares, now worth almost $735 million.
The company's stake in General Motors rose 10 percent to almost 33 million shares, currently worth $1.1 billion.
Berkshire also added slightly to its Wal-Mart shares, edging the stake 1 percent higher. That stake is now worth almost $4.4 billion.
It added 1.2 million shares of Chicago Bridge & Iron, bringing that stake to 10.7 million shares valued at more than $621 million.
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Berkshire slashed its holdings of Conoco Phillips by 88 percent to 1.3 million shares and sliced its Phillips 66 stake by 33 percent to 6.5 million shares. The stock it sold in those two companies is worth over $1 billion at Thursday's prices.
The company also cut DirecTV by almost $1 billion, shedding 32 percent of its stake. It held 23.5 million shares valued at almost $2 billion as of the end of June.
Liberty Media was reduced by 25 percent to 4 million shares, currently worth $194 million.
Berkshire eliminated its 1.9 million shares of Starz, a stake worth just $55 million at its current price.
A 1.8 million share stake in Now Inc. was created by a spinoff from one of Berkshire's established holdings, National Oilwell Varco.
The SEC filing does not indicate that anything has been kept confidential. In the past, Berkshire has asked for and received permission to withhold data on stocks it was in the process of accumulating so that copycats couldn't bid up prices.
—By CNBC's Alex Crippen. Follow him on Twitter: @alexcrippen