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MG MGB Technical - 12 volt batteries

I have a '71 BGT and will be converting the two 6 volt batteries to 12 volt. It has been suggested to me that I fit two 12 volt cells in parallel to boost the output, rather than just a single 12 volt.

Is this a good idea technically? If so, I have the following questions:-

Will the standard, but recently replaced, alternator generate sufficient output to keep both cells fully charged?

What is the required wiring diagram and what other battery leads might I need?
Andy

Andy

I replaced the batteies in the GT for two 12 Volt Exide batteies that i bought from a Fiat dealer. They were TIPO OEM parts. It is really a big difference!

There are no problems with the Alternator.

The wiring is simple, just connect both the + poles and both the - poles insted of the original wiring that runs from + to - of the interconnetion of the 6 volt blocks. New pole clamps should be used as the diameter of the + and - poles are not the same.

Ralph
Ralph

Thanks Ralph. I'll proceed with the conversion!

Andy
Andy

I'd say don't bother. A single 12v battery will give you all the cranking amps you need. Running 2 in parallel will give you: 2 more opportunities for corroded connections, 6 more cells that could fail, the opportunity to undercharge one battery whilst undercharging the other due to imbalance between them, etc. IOW, more chances for failure in exchange for no meaningful gain.

HTH!
Rob Edwards

Forgot to mention -- one battery is lighter than two! ;-)
Rob Edwards

Rob,

there is nothing wrong with your information. I took two and tried one first, then installed the second one a hour later. What a difference!
Easy starting, no worries if the fan is running on after the engine is switched off, no problems with electrical add ons anymore, just great. If my roadster would have two battery compartements, i would also fix two again.

Problems can come up when two different batteries are used. They must always be same capacity and the same age! For this reason i ordered them from a Garage and explained them that it would not help to take the one they had in stock and wait until another one was delivered!
Concerning failiure of a cell, i can not report any own experience. Not in the car and also not with different boats i had, not even have met someone who has had this happen, but i have allways and everywhere read about this. Seems to be a saga out of the early days of car electrics?

Ralph
Ralph

Two is just fine if you feel they perform better for you, but they are not necessary. Remember that battery design and construction has changed quite a bit since the days when our cars were new, and the need for two 6 volt batteries to meet the demands of most early MGBs, is obviated by today's single 12V batteries which usually out perform the combined 6V batteries of yore. That is why so many of us who have converted our twin 6V battery cars to a single 12V. If you have accessories or other devices you have added that truly exceed even a single 12V battery's specs, then by all means, go with two. Even with the multiplication of corrosion points, you will still probably be happier and meet your car's needs with two 12V units than just one.
Bob Muenchausen

We installed a new gel cell last year. Used the second battery compartment for a storage place. Mine is a 67. Have had absolutly no problems in cranking power or other issues.
BEC Cunha

Many years ago I changed my 2 6 volt batteries to a single 12 volt. It has worked beautifully for me. I think the battery size is a number 24 which just fits in the original box. Hook up was easy too. Positive line to the positive pole and negative grounded to the chassis. I see no need for two batteries at all. have fun!
Robert Ekstrand

I bought a single 12V 'calcium' (whatever that is supposed to mean...!) battery from Halfords and it turns my High Compression (10.5:1) engine over just fine. I'll look in the garage tomorrow night and get the code number - it was less than £60 if I recall. I'll check the label, but the Cold Cranking Amps were much higher than the two 6V it replaced and at half the price! Comes with a five year guarantee, too.. and a carrying handle to get it in and out of the battery compartment. Had to do a bit of filing to get it in, but it's in.

Of course it is a matter of opinion, but also a matter of experience. I too cannot see the point of two 12V batteries in parallel. If one is enough to turn over the engine (and it is) then one is enough.

Neil
Neil22

Turning the starter motor over is THE biggest single current draw our car's electrical system and battery ever face. The amount of time that this draw is used is very short in comparison to the amount of time the battery spends charging back up. Generally, even with high powered accessories and lighting demands, the current draw on the battery is not anywhere as large as for cranking the engine.

Just for informations sake, the last single 12V battery I replaced I had bought in 1998 and only replaced it last year. That is not bad service for a car which has been a daily driver, and says a lot about the necessity for a properly operating charging system in promoting longevity of your battery, perhaps more than the size or number of batteries in use in a normally configured car.
Bob Muenchausen

Bob,

in my 1975 roadster, there is a single 12 volt battery and no need for a second one, sure.
In the V8 things are a little different. The small 12 volt battery is able to start the engine and it works, but just try two of these in the V8 and you will relize the advantages when turning the key.

Ralph
Ralph

Ralph,
You were holding out on us -- you never mentioned you had a V8. More amps probably would benefit you (but did V8s have different batteries than 4 cyl cars from the factory?) Andy's 4 cyl (assuming that's what he's got) should be just fine with a single 12v....

For the record, CB cars (with twin batteries from the factory) can use a single group 26; RB cars (with only one battery box) take a group 24.

HTH!
Rob Edwards

Thanks everybody for your comments. An interesting mix of views. My '71 (4 cyl) does not have lots of power-drawing gadgets so, on balance, I'll settle with one 12 volt and save myself a few pounds! Happy motoring!
Andy

063 will fit the bins on a 71 GT(may have to trim excess trim around the base) I have two fitted in my GT with a 93 amp alternator I'm like a mobile power station:)
K Harris

Ralph,
You are quite right, but that's the reason V8 autos of all sorts generally come with larger capacity batteries in the first place. A higher torque requirement for the starter motor normally translates into a greater amp requirement at the battery.
Bob Muenchausen

In the UK, the battery of choice is the 063, apparently. Originally fitted to Rover 213/216 and Honda Civic, I believe.

I will be fitting one when the B goes back on the road. It was supposed to be this year, but is now likely to be next!
Dave O'Neill 2

It's an 063.
Neil
Neil22

... and here's the picture.
N

Neil22

Hi, Andy:

I just went thru some of this about a month ago.

I got a single 12 volt Group 26 Die Hard for $72 with the exchange for an old battery. The Sears model number is 30026. Everything works fine - of course, I don't have a V-8 engine.
Tom Fisher

I did the same as Tom--a Sears Die Hard group 26 which is better than the two 6 volts.

Here's another option if you're interested in reliability and not originality--get the $300 hi-torque gear drive starter. Mine draws about 30 amps when starting. An original MGB starter in good condition probably draws 40 to 50 amps, maybe more. Instead of making monstrous battery upgrades, make a huge improvement in the starter. Like Bob M. says, the starter is the biggest draw on the system. When you upgrade the starter, there's not such a drastic need for a battery upgrade.
Ken
Kenneth Thompson

Just for your info, the battery I mentioned that I had replaced was also a Sears Diehard, and it was replaced with another. There have been many comments on this BBS and others, and ratings in magazines that the Diehard is not the ultimate battery you can buy, and a good buy with even better ratings are those that can be had from Walmart. However, given my experience with the unit I had, I would say that regardless of what brand you settle on, it is the performance of the charging circuit that will ensure that they live their max. life and perform at their best. Sometimes, poor performance in the past is not so much the battery's fault as much as it points to a poorly performing charging system.
Bob Muenchausen

If you have a generator model dual batteries have the advantage of greater amp-hour capacity. Since the generator cars don't charge at low rpm the factory compensated with battery amp-hr capacity and a deeper draw down design.

That said my 65 generator model has a single 12v works fine in moderate traffic. But after a lot of stop and go the lights get dimmer until things get recharged.

The calcium mentioned above is probably calcium doped plates used to create low maintenance batteries. A disadvantage of these is deep disharging cuts the life.
Robert McCoy

This thread was discussed between 02/09/2007 and 10/09/2007

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