What battery do I need?

Kevin,

My 1969 Mercury has 12 volt electrics and the Lucas battery is supposed to be Lucas PUZ5A which is 8 Ah. 

Currently I have a Numax battery fitted i.e. Model YB9B, which is 12V and 9 Amp hour.  Previously I used a Rob Hunter 12N9 3B. 

I've modified the battery retaining "clamp" by using some 6mm studding to fix to the back of the battery box, covered the thread where it is beside the battery with some rubber or plastic tube, then made a small flat plate to clamp the battery, and hold this in place with a couple of 6mm wingnuts.

Lots of batteries will work.  If only a box  with no securing hooks ,all it matters that it fits in,terminals are the right way round and screws can be accessed from the front., a bit of foam packing is what most have .Best if the battery is properly secured on a nice soft rubber base

I have always said that 5 AHR is the minimum size. So 7 or 9 or even 11 Ahr would fit. The next criteria is can it fit in the 'Dommie' battery box, without rubbing on metal? Old inner tube rubber is very useful and even blocks of wood, as it soaks up any acid and is easy expendable.

Very square edged batteries with often 1/4 Lucars as the terminals are often from the alarm world and are to be avoided. Invariable the charge rate from a motorcycle is greater that the alarm battery wants and therefore it dries out very soon.

Hi Kevin,

Once you have decided on the physical size, I would highly recommend finding a MotoBatt of that size as you do not need to worry about acid.

http://www.motobatt.com/index.php

Or similar.

Tony

Motobatt do a 5ah battery which fits, very small, does the trick