Old style DeWalt tools with a new style battery

I bought some DeWalt 18v tools about a dozen years ago... I'm not a pro carpenter, so for my lite duty house projects the tools have lasted and still work well
.
Not so the batteries... they won't hold a charge for very long so I've been looking at replacements
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I also have some newer DeWalt 20v tools (different tools)
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While looking on Amazon (hardware store I go to doesn't stock the 18v batteries since the tools are old) I discovered an adapter that plugs into the old style tool and accepts a new style battery
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So now I only have to keep up with charging one style of battery for old and new tools
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https://www.amazon.com/Biswaye-Battery-Adapter-DCA1820-Convert/dp/B074V7QPTJ