Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB GT V8 Factory Originals Technical - Battery Choice

Assuming I can find one to fit in a single chrome bumper battery box (!), what would you say should be the minimum amps I should go for in a battery to power my V8.

It's normally carbed and otherwise standard.

Liam H

I should add, my alternator is either 55 or 65 amp. I cant be sure as it is not with me at the minute! Don't ask.
Liam H

An Optima can be made to fit.
Jim Blackwood

Liam, another option to increase amps is to install two 12 volt batteries, one in each cavity. Make sure each battery has it's own individual ground. Then run the positive lead from the drivers side battery to the positive lead on the passenger side. I've had this setup on my 4.3 V6 for years and it works great.
Mike Maloney

A "Group 26" battery will fit very neatly into a single chrome-bumper MGB battery box without modifying any sheet metal. You might have to modify battery cables... but that's easy work and besides your car would probably benefit from nice new cable.

While you're at it, it's always good advice to fit a battery disconnect switch near the battery. (Benefits include that you can shut down the whole electrical system in the event of an accident to prevent fire, and you can easily completely eliminate discharge of the battery by parasitic loads when the car isn't being driven.) I prefer to use one battery in the passenger-side box to offset the driver's weight.

IMHO, most of the engines people on this BBS have should be easy to start with just about any healthy car battery... assuming the engine is properly tuned up. In the grand scheme of things, these are not big engines. In really cold weather, they usually stay in the garage. If you're running a high-compression ratio or you drive your car all winter, you can disregard this advice.

Battery manufacturers like to put performance numbers on their products... things like "cold cranking amps", "amp hours" or "reserve capacity". Sortof like wattage ratings on stereo equipment... they have only marginal value for comparing one battery versus another within ONE manufacturer's product line. You might think "pick the one with the most cold cranking amps!", but even that isn't necessarily good advice because battery design is a compromise. You get more cranking amps by making the battery plates thinner, so that you can fit more pairs of battery plates into the battery case. Thinner plates suffer more from expansion and contraction when the battery is used, and therefore typically contribute to shorter battery life. Thicker plates give more reserve capacity.

55 or 65 amps, your alternator should be plenty big to recharge the battery. (My alternator is much smaller. It came off a little Suzuki engine and I love how lightweight it is.) Keep in mind that voltage-drop in cables can be significant... for good starting and charging you need well-maintained cables and connections, and they need to be adequately sized.

Get the largest battery cable available, it's going to be rather long ~6-8'. Try a boat shop. Then use the largest group 26 you can get. More expensive brands are better batteries as a rule. One is quite adequate. I'd go with the longer warrantied ones. You can buy a Champion, they're only good for a year or buy an Optima and forget it for a decade. Your choice. The Optima is cheaper by half.
Jim Blackwood


last year I had to change the two 6 Volt blocks and took two Exide from Fiat, that are spare parts for the Tipo. They are priced nearly equal to the discount offers but are of far better quality and drop right into the compartments. They are rated 48 AH each, I think.
For starting and driving only one will do, but if the consumption of the twin fans (I wired them to run on after the ignition is cut off until 80 deg. cent. of water is reached) come in to mind, two of them makes a real difference in restarting.
I also did not need to recharge the batteries after some month during the winer rest.
The batteries are simply wired (+) to (+) and (-) to (-). They are charged by a 55 Amps Bosch alternater that came from an old BMW.


I only have one battery box! the other was not replaced during the restoration.

The question was more about whether there was a minimum specification of battery I should go for.

I'm sure I can find one to fit, I just want to make sure it is powerful enough and wasn't sure what to look for.


350 to 400 cold-cranking amps is what you want to look for, and that's easy to find, most common. Personally, I'm gonna go with one of the dry cells when I get there. Joe
Joe Ullman

I started a long ramble of explanation, but decided it was too boring.

I use Optima batteries in all my trucks, etc. But tried this little battery out as a smaller alternative for my 65 race car.

Check out:

First I used it around the shop as a carry around power source for testing an electric fuel pump. Then it got used to start the sick TR8, I'm working on. It started that car up about 20 times with no problem.

475cca in a package 5" x 7" weighing 25lbs

I'm pretty impressed.

Moss carries them for the Miata, or they are available from other dealers.

KJ Dodd

FWIW, I've always bought the cheapest battery from Walmart that will physically fit in everything from 1275cc Minis to S10 Blazers with the 4.3 V6. Can't complain.

Derek Nicholson

I purchased a dry cell battery after a lot of searching one that would fit without modifications and have enough AMPs to crank a high performance engine. I have the mfg at home and would be glad to provide the model and mfg. It fits great and cranks the engine great. The best thing is NO acid and no issues of eating metal and paint.

Only issue is the cost. They are $150 plus.

Jeff Howell, 63 B
Jeff Howell

Optima Red Top! Monster of a battery!

Finally found one with 620 cold cranking amps and a 4 year warranty, a little enlarging of the battery box should see it fit.


I measured the space, went to KMart and bought the most expensive one that would fit. Objective, get the best of the generic, readly availiable.
The battery isolater is a great idea. I have one. A green screw down switch/knob, very simple.It means that if you go away for periods of time,as I do, you will always be able to start the car. Also when working on the electrics,or welding, it makes it very easy.
I know you can undo the lead easily enough but it is not as easy as turning a knob, & you tend not to bother.

This thread was discussed between 17/05/2006 and 26/05/2006

MG MGB GT V8 Factory Originals Technical index

This thread is from the archive. The Live MG MGB GT V8 Factory Originals Technical BBS is active now.