In the words of Anthony Curzon...
"The PUZ5A has a feature that owners of the P11 series should be aware of: the battery posts are screwed into the top of the battery. This is very important to P11 owners as the author experienced one day when crossing Clapham Common in South London. The later Japanese batteries have their posts on their sides, so the battery connections subjected to vibration, can earth onto the battery cover, and the engine would cut out, intermittently. The cure is to always face the batteries side terminals away from the cover, or towards the oil tank, and this annoying occurrence cannot happen. Also, if you can obtain an original Lucas PUZ5A, then this would not have happened in the first place."