The best replacement for 24v is 12v.

The best alternatives to 24v are rated as following:
★★★★★  12v
★★★★  12v cummins
★★★  12v trolling motor
★★★  12v solar
★★  common rail
★★  12v solar system
★★  48v
★★  12v inverter
★★  18v drill
★★  12v vr6
★  12v led
★  12v led strip
★  12v battery bank
★  12v winch
  12v solar panels
  18v
  36v
  12v land cruiser
  16v

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Speaking about 24v, one probably shouldn't forget about atx power supply.

Other search terms related to 24v and their ratings are:
★★★★★ atx power supply
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24v
12v
12v cummins