Most of the energy loss is due to the chemical processes not IR loss. There is what is called a 'kinetic' energy requirement to upset the equilibrium when current flow is required. There is a voltage potential consumed to create this kinetic movement. This includes moving electrolyte around, transfer of molecules, cracking molecules down and transfer of ions.
In the last 10 to 15% of recharging some water molecules in the electrolyte are separated to hydrogen at negative plates and oxygen at positive plates. This process consumes energy and creates some heat.
Overall, a lead acid battery will take 10-15% more energy to recharge it over what was taken out during discharge. Much of the loss occurs in the top off phase of charging.