I had this while on holiday, far from help.
In my case it turned out to be a broken wire on the alternator - my guess is this wasn't telling the battery that the alternator was working - and my further guess is it was trying to 'save' the battery by not using it to power non-vital items, such as pull up the step. This theory was backed up by the engine racing on tickover as if it was trying to compensate and charge the battery. Anyway, I fixed the (very thin and hard to see) wire on the alternator and it has been fine since.
Steve h, November 2014