We all know the usual (simplistic) model for batteries, that is, representing it by a pure constant voltage source in series with its "internal resistance". This is probably sufficiently precise for many applications during a relatively short time. I think this model (implicitly ? / not at all?) assumes that the battery is discharging into some load, or what is the same, that the current is flowing from the + terminal to the - terminal. But let us assume that we have a rechargeable battery (say a lead acid battery) and, for the sake of simplicity, that is it is fully charged (so that the pure voltage source of the model cannot much increase its voltage). To put flesh on bone, let us assume its voltage is 12 V.
If this battery is submitted to a somewhat higher voltage in the reverse direction, say +17V at its + terminal, is the above model still approximately valid ?