If you accept low efficiency, you can use thermal machines (max efficiency of roughly 35%), you can DIY such liquid battery : molten wax and a Stirling engine.

If you accept low efficiency, you can use thermal machines (max efficiency of roughly 35%), you can DIY such liquid battery : molten wax and a Stirling engine. Melt the wax to charge, and store in a thermos. You can use heat pumps to increase the efficiency by recovering wasted heat. Plenty of things are technologically possible but as energy storage is commoditized so outside the lab we only care for the best ones where cost, efficiency, energy density, power density, energy leakage and battery life define the Pareto frontier. There are flow batteries where you can switch the electrolytes when they are discharged. You can also use standard lead-acid gel battery and switch them when they are discharged. (Use multiple small batteries and discharge them sequentially). You can also switch solid-state Li-ion batteries. There are also some molten metal and salts batteries : for example Ambri (https://ambri.com/technology/ https://ambri.com/technology/) (https://www.youtube.com/watch?v=m8751tkBU_Q https://www.youtube.com/watch?v=m8751tkBU_Q) make some liquid metal battery ( where the discharged state is an alloy, and charging the battery separate back to its original components. Their batteries work at 500°C and are 80% efficient (vs lithium 95% efficient), and need to be immobile when used, but other can work at room temperature.