If you are not quite ready to purchase new 18V tools but want to breathe some new life into what you have, check out the DeWalt DC9180C Li-ion batteries.
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Battery Adapter for Makita DCA1820 18V Compatible for Makita Lithium Battery to for DeWalt CA1820 18V DC9180 DC9096 Tool Use - AliExpress
2x 18V 2000mAh XRP Lithium Ion Battery for DeWalt DC9182, Dc9181, DC9180, Size: Dimensions: 4.25x3.5x4.75, Black
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18v li-ion Battery for Dewalt DC9180 DC9096 DE9096 DC9098 DE9039 DE9095 DE9096 DE9098 DW9095 DW9096 DW9098 with Charger - AliExpress
DCA1820 for Milwaukee 18V li-ion battery convert for Dewalt old 18V nicad DC9096 DC9180 - AliExpress