Can a 24V lithium battery run 12V equipment through a step-down converter?

Direct answer: Yes. A DC-DC step-down converter rated for the combined 12V load current, with an input range that covers the battery’s full voltage range, is the standard solution. Fuse the converter input at the battery side and its output at the 12V distribution. Do not take 12V from the middle of a 24V string made of two 12V batteries; that unbalances them.

Battery voltage range. The 24V 100Ah lists 25.6V nominal, 29.2V maximum charge and 20V cut-off, 100A continuous and 200A peak for 3 seconds. The 24V 200Ah lists the same voltage window with 100A to 200A versions. The 24V 100Ah EU thin size lists 552 × 110 × 288 mm, 21 kg and 100A. A converter should accept at least 20V to 30V input to work across the whole range.

Sizing the converter. Add the current of all 12V loads that can run together, including motor start currents such as pumps, and choose a converter rated above that continuous figure with a margin of about 25%. Radios on transmit and fridge compressors starting are common peaks.

Isolated or non-isolated. Non-isolated converters share the negative; isolated converters separate the 12V system from the 24V system. Boats and vehicles where the 12V negative is bonded to the 24V negative usually use non-isolated types; where electronics need isolation, choose isolated. Follow the installation’s grounding scheme.

Efficiency and standby. Converters lose some energy as heat and draw standby current. For loads running all day, include converter losses in the energy budget, and switch the converter off when the system is stored.

Protection. Fuse the converter input close to the battery and the output at the 12V distribution panel; size cables for the current at each voltage. See DC-DC converter basics.

Why not tap a series string. With two 12V batteries in series, drawing 12V from one battery discharges it more than the other, and the charger cannot correct it. This is a common cause of early failure; see two 12V in series vs one 24V.

Several converters. Large systems often split 12V loads across two converters, so a converter failure does not take out navigation and pumps together.