The technique described in this paper balances the power and energy withdrawn from a battery in galvanostatic discharge control that aims for stabilisation of the electrolyte concentration above the depletion level. This aim is achieved with relatively simple proportional feedback controls that are exponentially stabilising controls for a simple diffusion process that is the core part of battery processes. Although the full mapping of the proposed controls to state is rather complex, it has shown that the transformation works. In practice, these controls can be approximated either with the integrated past controls or with a simple exponential function that depends on a few parameters adjusted to the electrochemical processes in a battery under consideration. The battery control is tested in simulation on a detailed model developed for a lead-acid electrochemical cell.