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MG MGB Technical - Battery Fit

I grew tired of battery acid leaking on my 1972B. The previous owner had converted to 12V, and I replaced the battery for the 2nd time in 8 years a year ago. Each fall, I found the metal hold down fittings and the base of the box were corroded, so this year I removed the corrosion and decided to install a plastic battery box. The box fits the car correctly, but the Group 26 battery doesn't fit the box that was designed to hold a 6V battery. (large by about 3/4 inch). I believe it is the protruding hold down flanges on the battery on all sides, intended for mounting that is giving me the problem. Any suggestion as to brand of battery (Group 26 or alternate size?) that will fit into one of these plastic boxes? I purchased the box from the Roadster Factory, but I imagine they are all the same.
Joe

Two years ago, I had the same problem fitting a new 12V Napa battery into my '74. It took less than a minute to grind off the hold down flanges with a 4" mini-grinder. Then the battery fit perfectly.
Kim Tonry

I recall someone mentioning the Miata battery in another post...check the achieves...supposed to be smaller than the group 26...
Bob Dougherty

Hello,

Go to that site to find the model suitable. Some B owners are found of Garden tractor 12V battery with 300 AMP reserve.

Cheers,

Jean G.

http://www.rtpnet.org/~teaa/bcigroup.html
Jean Guy Catford

One of the many drawbacks of fitting the so-called 'battery boxes'. Some say to cut off the flanges, but that will nullify the gurantee on a new battery. But I don't understand why you are getting leaking acid anyway, unless the batteries are capable of being topped-up and you are overfilling them, and I thought most modern 12v batteries were 'sealed' these days.
Paul Hunt

I swapped the battery in my 80LE recently and had to do some research to get the correct group size. There are some discussions in the archives, but the battery tray sizes are different for the twin 6Vs and the later 12V MGBs and you'll be considering your battery bix as well. Thus, some conclusions in the archive discussions can be misleading. Like Jean mentioned above, your best bet is to do some measurements and "google" search for "BCI battery group sizes". You'll find a table showing all dimensions, height, width, length for all groups. Note that the dimensions don't include the hold down ears on some batteries, but not all batteries have them. Also, note your positive/negative post layout. You can buy a group 34, for eaxample, or a 34R with the posts reversed. Using the BCI chart, you should be able to confidently buy the battery group size that fits your particular application.
Rick Penland

Joe, check the voltage of your system with the car running at about 2000 rpm. If you are seeing over 14.6 Volts, the water and acid is being cooked out due to too high of a charging voltage. This may also be causing the short battery life.
John H

I went to my local Interstate Battery Store today, and found the Miata battery a perfect fit. It is also a sealed battery, due to the fact that in a Miata it would be inside the car as well. It came with an external vent kit, so I won't be breathing acid fumes and should provide enough cranking amps for the warm weather driving I do with my B. Thanks all for your comments.

Joe
Joe

The maximum permissable alternator charging voltage is 14.7v, MGB dynamo systems charge at up to 15.5v, and I'm told TDs charge at up to 16.7v. So 'over 14.6v' but within those limits certainly isn't going to damage the battery.

Whilst the higher voltages of dynamo cars may well result in more topping-up needed, they don't lose acid, only water.
Paul Hunt

Westco batteries, as found in Miatas, are a perfect fit in the plastic battery bins. In fact you'll have plenty of room left over! As an added bonus, the batteries are lighter, hold a charge longer and will not spill anything even if mounted upside-down. You can buy them from Moss Motors as well as dozens of other retailers. If you shop around you can find them as low as $80. I have them mounted in two of my M.G.s.
Steve Simmons

This thread was discussed between 06/01/2009 and 07/01/2009

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