Fitting a 12 volt battery to a chrome bumpered MGBGTV8

Gordon Hesketh-Jones (Harvest Gold 1904) from Cornwall has changed from the original twin 6 volt batteries and describes how to carry out this modification. (Mar 02)

The twin six volt batteries fitted to the earlier MGBs are now quite difficult to obtain outside MG specialist parts traders and as they are an obsolete slow-selling design which no longer benefits from the technical progress and development seen in 12 volt batteries. Also six volt battery prices do not seem to benefit from the competitive market forces which apply to 12 volt batteries. I cover a high annual mileage with my MGBGTV8 and have found the 6 volt units rarely lasted more than 2 or 3 months beyond the 12 month warranty. I also found the need for the regular removal of the rear seat and metal access panel in order to top up these old- fashioned batteries was irritating.

Some twelve years ago I decided to replace the pair of 6 volt batteries in my V8 with a single 12 volt battery and found that with a little modification to one of the battery trays, a standard "065" battery would fit. The "065" refers to the physical size of the battery as defined by UK standards, and all manufacturers fit different sets of plates - for example medium-duty, heavy-duty, caravan-duty etc into these standard cases. The 065 case is no higher than the standard 6v battery, but is longer so I had to modify the battery tray by flattening the forward retaining cross-member part of the tray. One standard battery clamp was fitted to the rear of the battery and a second was modified so that that it sits across the centre of the battery i.e., from side to side; this is a practical solution because a clamp located at the front of the 065 battery could not easily be reached, and in any case the battery is sealed for life.

My own choice was to fit the 12 volt battery to the nearside battery box, but as the existing heavy-duty cable carrying the main 12v lead to the starter would not quite reach to the new battery position, I used a small "dough-nut" rubber mounting as the jointing point for the standard cable and for the extension cable. This technique safely isolated the live 12 volt supply from the chassis. The rubber mounting used was approximately 1inch diameter and 1inch long with metal plates at each end carrying screws threaded ¼UNF and they can be obtained from any car exhaust specialist. I located the rubber mounting in the off-side battery box then used the existing cable formerly used to connect the two batteries together for the connection to the 12v battery, this having the benefit that the existing cross-cable is already protected inside a metal tube. The earth connection is already in the near-side battery box, but I replaced this with a new earth lead with a side clamp, rather than the old top-hat fixing; a similar change was made to the clamp on the cross-over lead for the positive terminal.

Loading and unloading the battery from its box on the V8 can be made easier using a either a permanent rope sling fixed around the lower part of the 12 volt battery or a purpose made battery lifter can be used - see V8 Workshop Notes 224 and 225 in Volume 6.

An appropriate heavy duty battery in this standard case will have a cold cranking capacity of between 495 and 605 amperes depending on the supplier (and the price paid) which is usefully greater than the combined current of a pair of the many commonly available 6v batteries which were rated at 480 to sometimes 500amps. So the 065 is a suitable choice as its performance reserve is a match to that of the original specification of twin 6volt batteries.

More importantly, the new batteries are sealed for life so you do not have to keep delving beneath the rear seat and access panel to top them up. In my experience the 12 volt units have all lasted for more than four years so there has been a good saving in cost as even heavy-duty 12 volt batteries can be found for around £40 plus VAT compared with around £58 plus VAT each for the 6 volt version. The performance and price figures for new Exide batteries were obtained from ATS as a national chain of UK suppliers, and they recommend a minimum cold cranking current of 495amps for our V8 engines. The current 065 batteries supplied by ATS now incorporate a lifting handle and are rated at 495 amps.

A major benefit of making this change, particularly if you use the car for long-distance UK or continental touring, is that the empty battery carrier box (on the offside in my case) can then be lined with marine plywood (or aluminium or steel, to your choice) to

provide an excellent carrying space for essential V8 spares you need to carry if travelling long distances in a classic car - choke cable, accelerator cable, distributor points, condensers, light bulbs, fuel pump, alternator, first aid kit for example. The amount of extra carrying space is quite incredible and vital in a two-seat car. Now that the RAC and AA mobile patrols no longer carry points and condensers or similar consumables in their vans, carrying your own spares has become even more important.

Another modification is also possible if you have made this 12 volt battery modification in the nearside battery box - you can relocate your petrol pump to a higher position away from the road dirt in the wheel arch if you have had problems in this respect. The fuel pump is relocated below an intermediate panel. The space above that panel can be made into a lined battery box in which tools and spares can be stored.

Sequel from Gordon Hesketh-Jones (May 02).
My battery recently died suddenly and totally and would barely light up the ignition light! Fortunately this happened after I had re-loaded our luggage into the car outside the hotel near Dover. So after the RAC had jump started the engine, I was able to drive to ATS at Folkstone for a new unit and we were able to catch the next Eurotunnel shuttle. Obviously the sudden and catastrophic failure was irritating at the time but at least the failure happened in the UK and not half-way up an Alpine pass! There had been no warning of the impending failure - no slowness in the starter for example - but at least I had had four years and 50 to 60,000 miles of use from the battery so I can't complain.

Footnote: Gordon had recently done the Lands End to John o' Groats event and was on his way to another rally in Sicily when the battery failure occurred at Dover. He mentions that "in Sicily I met Walter Kallenburg who send his regards. Walter has the ex-Malcolm Beer racing V8, now at 4.2litres, but was in Sicily in his TF1500. I also met Gerhard Meyer who used to own a USA export version of the MGBGTV8 for ten years - apparently seven were shipped to the USA but were never taken off the boat as the importers decided they wanted Triumph Stags instead! Some people have no taste at all. The seven V8s returned to the UK and Gerhard's car was loaned to someone for use on an RAC rally, where it did a "straight-on at a tree" on the first stage. That car plus another new but crashed V8 were bought by an Abingdon employee who advertised the pair in Motor Sport. Gerhard bought his and after 18 months collected a virtually new and totally rebuilt rubber bumpered V8 with a complete photographic record of the rebuild. After ten years, the German government put a horrendous tax on non-catalysed large engine capacity cars so Gerhard sold it and bought an MGA MkII instead. Two years later the German government took the tax off classic cars so Gerhard was very frustrated!

Clarification of the current rating on car batteries Brian Moyse (RV8 BRG 1714) provided a useful clarification of the current ratings on car batteries - for example 480A. "The value given on the rating plate is the Cold Starting Performance or Cold Cranking Current which is defined as follows (courtesy of Varta Batteries at their very useful website) - cold cranking is the discharge current given by the manufacturer. It is emitted by a battery at a temperature of -18oC with a minimum voltage of Ui = 7.5 volt for a period of 10 seconds, according to the EN specifications - I can recommend a look at Varta's website where they have a Q&A section and a full glossary of terms related to all types of batteries including car batteries.
Use the offside battery compartment says Geoff Allen who provides a further useful sequel
"I have carried out a number of modifications to the batteries on chrome bumpered MGBs and V8s and have put the replacement 12 volt battery in the offside battery compartment. Then all you need do is make up a new earth lead, drill the body and bolt on that lead to make a good earth connection within the offside battery compartment. You can disregard the cable linking the two compartments which passes through the propshaft tunnel but it's not worth attempting to remove it. You can leave or remove the original earth lead in the nearside battery compartment."

Copyright reserved by the V8 Register