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MG MGB Technical - battery problems

well after pulling my car out of the garage for the fist time since last October gone to start it and the battery's are as dead as a dodo.

now last year i bought to new 6 volt battery's 140!
i was sort of expecting them to be flat but just thought i,d take them back as there still under guarantee

but now i cant find the receipt for when i bought them.
without this there's no point in me taking them back really peed off now.

anyway I've read somewhere last year just after buying them that a 12 volt battery will fit in one of the boxes and work as normal.

but i cant remember what the battery was off or the part number.

anyone done this or shine a light on the subject?

s truman

Type 063 seems to be the best choice of 12 volt battery, it's widely available and fits snuggly into one of the 6 volt battery bins.
If you fit the battery into the driver's side (RHD car) bin you'll just need to either fit a new battery earth lead or fit a longer one to the existing fixing point. You might also need to alter the battery clamp, but a cheap, generic one from a local autoparts store will work fine.

I recently bought a Type 063 battery online from for 34.99 delivered. It was delivered next day and thus far appears to be a good quality battery.

mr truman, I have just converted to 12v for the second time(1970 BGT). The battery that fits in with out any fabrication I found to be to small in terms of amp hout and cold cranking speed.The battery I purchased is an Exide Premium (EA 530) 53 AMP HOUR/540 C.C.S (200z170x185 high)It did need a bit of fabrication to the front edge of the passenger side battery space but nothing too dramatic,I removed a strip OF metal 7" X 1/2" and the battery drops in sideways with the posts near the centre of the hole. It still allows you to use the clamps to secure the battery, and the cover plate still fits over. Peter
p j mayo

I've left mine 3 months and they still started the car, only a bit slower than normal. Since October is quite a bit longer than that granted, but I still wouldn't expect them to be completely dead. I'd be looking for a drain, and in future run the engine every month or so in winter!

Have you tried charging them? Whilst they may now be damaged and not hold a charge like they should, you should still be able to get some use out of them, and sulphation tablets (like headache tablets they cure, not cause) seem to be around again. If you can get a charger that charges at 15v or so, that will put more capacity back in them rather than the 14.7v or lower from an alternator.
Paul Hunt 2010

haven't tried charge them i don't have a 6 volt charger
bump started the car and drove it home 30 miles tuned it off and nothing.
i would have thought they would have charged on the way home so a point.
also had a new alternator fitted last year.
after the expense of buying them last year im a bit gutted to be honest but i thing im going to go down the single 12 volt battery route.
is there anything else that needs doing or is it just play and play so to speak.
s truman


Firstly you don't need a 6 volt charger. You charge both batteries in series (i.e. 12 volts), so use a 12 volt charger. As I don't use my B often enough (the F needs are run as well occasionally), I fitted an isolator switch on the heel board immediately behind the driver's seat. I disconnect after every outing. Even leaving the car unused for several months the car has always started. I don't have a radio or clock in the car to worry about, but if you have a radio you will need to have the code to hand.

I also disconnect the battery in the F, and also have had no problems when left for weeks on end during the winter.


W A Nixson

I do not remember if you can charge both batteries together at 12V (the system voltage they produce in series) or not. It has been a long time since I switched over to a single 12V. But, I believe it was possible to do. Perhaps Paul Hunt can comment on this.

If you batteries were dead after starting the car and driving it for 30 miles you were either running off of the batteries (alternator not producing current) or you have bad connections which did not allow the properly working alternator to charge up the batteries. I would clean up all of the connections, disconnect the ground strap between the battery and chassis, charge them in series, then see what happens. It is possible that one, or both, batteries have died, in which case you will need to replace them. But, I am not sure you have an actual battery problem yet.

Les Bengtson

I use a Mazda Miata battery. Fits easily into one of the 6 volt battery bins.
Bernie Lowe

A 30 mile run will do little for deeply discharged batteries.

You can charge them in series but because of their state I would first put the 12volt charger on low charge directly onto one 6volt battery until it starts to take a charge, do the same to the other battery and then connect them in series and put them on high charge.

It may take several days to get them to be fully charged but they will recover.
Chris at Octarine Services

And for next winter buy one of those battery maintenance chargers that you can leave permanently connected. These gadgets keep the battery(s) in tip-top condition during the lay-up period. I used one last winter and it was brilliant. The car started as if it had only been left for a day, not several months.
Mike Howlett

You can charge batteries in series, if you think about it each battery is three or six cells in series, having three cells in one case and three in another is irrelevant. Charging each 6v from a 12v charger on low is a good idea, they need a bit of welly to get the capacity back. A few years ago Mercedes were having to select alternator regulators with voltages at the upper end of the tolerance, as those at the lower end weren't putting enough back in even a partially discharged battery and batteries were 'failing' prematurely.

If you bump-started the car they weren't completely flat or anywhere near, just too low to crank, and will be fine after a decent charge. A friend recently did completely flatten his when his ignition relay stuck on and no amount of towing up the road would get it started, it needed jump-leads.

I have cut-off switches on all my cars, even the ZS as in summer that can be unused for 2 or 3 weeks at a time. The first to get one was the V8 as I found it's alarm was flattening the battery in a couple of weeks and knackering it in 18 months. The roadster got one next, primarily as a security and safety device - with the amount of unfused wiring on an MGB you don't want to have to be fiddling with tools, battery cover and battery connectors all the while your wiring is merrily burning.
Paul Hunt 2010

I have a 12 volt Battery Tender fitted to my '67 that is still using twin 6 volt batteries. The car sits idle for months, but always starts right up when pressed into service. The battery charger is connected to the positive terminal of one battery and to the negative terminal of the other. My last pair of batteries lasted 13 years. RAY
rjm RAY

I've just measured a Halfords 063 12V battery and I reckon it's too big. The longest length of the base is 207mm and my B has only 200mm available. Ok, you can shave off the base securing lugs to get to about 195mm but would the securing clamp and stays fit?
The alternative from Halfords is an HB202 which has base dimensions of 175x175mm, but the cca is lower at 340A. It is about 190mm tall but looks as if that would be ok. Anyone tried this one?
Richard Coombs

The 063 definitely fits. Mind you it has to be tilted at an angle in order to insert it into the opening but fit it does and is more than man enough for the job.
Iain MacKintosh

My 73 roadster came with a 12v battery, and when that failed and I tried to get it out I discovered it was bigger than the opening. I had to tilt it right over onto its end to get it out, fortunately it was sealed. The cradle had been modified to take that, and at first I thought they had welded the cradle in around the battery!

Be careful chopping the lugs off, it will nullify the guarantee if they notice.

I've got a cigar-light plug on the end of my charger, so it is simplicity itself to plug it into the lighter socket, which is permanently powered and fused. Only fitted to all cars from 73, before that it was optional and could be wired to the same purple circuit, the accessories circuit (fused but you need the key in), or the brown circuit (unfused). In these cases clipping to the purple end of the bottom fuse is going to be easier than lifting the battery cover.
Paul Hunt 2010

If the type 063 is a bit tight, rather than trim off the lugs use a couple of pieces of wood underneath to raise the height. The battery cages are tapered so you will have more clearance if the battery is raised 1/2 inch. Make sure the is enough clearance from the top of the battery to the metal cover to avoid shorting and make sure the battery is firmly clamped in.

Aside from providing a mounting flange for some cars, the lugs will also add to the strength of the battery casing. You're tempting fate cutting them off, and as Paul says your warranty will be voided.

Hi Paul. What did you replace your old 12V battery with?
Richard Coombs

Hi Chaps
Go to MGC and look at Battery for MGC.
you will find a lot of info there,
that should sort your agro.
have a read of my last post.

Tim Hodgkinson

Richard - twin 6v :o) I think this is only the 2nd set in 20 years, although I've had these quite a long time now.
Paul Hunt 2010

I am a loss to understand why anyone would go for a battery that doesn't fit without either modifying the battery or the battery frame. The 063's I've reviewed require both to fit my car.
There are several batteries around with a 175x175 base dimension and a height of less than 200, and which have capacity and cca to spare.
I'm going for a Bosch 4000 (175x175x190, 42Ah, cca of 390). Cheapest I've seen is about 55 including p&p.
Richard Coombs

well just been out to take the battery's off the car and found one of the battery terminals has cracked.
sort of held it in place and the car did turn over be it very slowly.
so i think i,l try the suggestion and put them on a trickle charge fore a few days and go from there.
thanks for the reply's so far.
s truman

One of mine cracked the case adjacent to the terminal, obviously let out gases as the terminal and clamp was completely covered in green fungus (see below) and that cell was quite a bit down. Cleaned it off (and put a rust stain on the drive that is only starting to fade after several years!) and Araldited the crack and it has been fine since. It had eaten into the link cable clamp quite a bit so I replaced that with one of the correct armoured ones, but that was a bit shorter so I had to turn the battery round. That meant the +ve cable wouldn't reach, but I have a battery cut-off switch right by that battery so it was a relatively easy job to replace that short section ... with the good end of the old link cable!

If ever you replace or fit a link cable make sure you support it with the original clip that is situated high up between the two batteries, as without that it will rest on the prop-shaft. How do I know this? shortly after going back to twin 6v, which required a new link cable, for some reason I decided to take it back out and have a look, and found the insulation worn half through.

Paul Hunt 2010

I once had an MGA towed into the shop that had lost all power. After raising the car up on the lift, there was nothing left of the batteries and their cages except the terminal ends. The cages had rusted completely out and the batteries had fallen on to the road destroying them instantly. I only wish that I had a camera available at the time. It was quite nerve wracking to see. RAY
rjm RAY

The opposite of this, then, where the driver had run over a mattress. The springs got wrapped round the propshaft, punctured the tank, and it was only when the car ran out of petrol that the driver (said to be a woman, but I wouldn't know) did anything about it.

Paul Hunt 2010

Paul, that's one for the books. RAY
rjm RAY

well it seems you cannot charge a 6 volt battery with a 12 volt charger! within seconds of turning on my charger it started to smoke!

apparently its not the volts that mater its down to the amp age.
s truman

Did you charge the batteries, while connected in series, or did you try to charge a single battery? I can see a problem when only charging a single, 6V, battery with a 12V charger. But, if you were charging the two batteries connected in series, the smoke would indicate that the battery was defective. At least as I remember doing such things long ago.

Les Bengtson

What smoked - the battery, the charger or its leads? I'd have expected too much current to have blown the output fuse ... if it has one.

It's volts that are important, it's the voltage difference that creates the current. Chargers output a voltage, the current that flows will be dependant on several factors. Chris did say to put it on low charge, if the charger isn't switcheable then perhaps it's not such a good idea. But it's still worth pursuing but with some resistance is series, possibly an old headlight bulb, or a coil, or maybe just some lengths of thin wire. Measure the voltage at the 6v battery and if that rapidly rises above 16v then you need a bit more resistance. You also need to connect +ve to +ve, and not +ve to -ve ...

However a friend completely flattened his battery when his ignition relay stuck on, but even with that sorted his radio was faulty and seemed to be flattening it. After normal charging, and disconnecting the radio, just driving it round seems to have put enough into the battery to give normal cranking speeds over several nights and it starts as before. May still not have the capacity to keep cranking if there were something else preventing it from starting though.
Paul Hunt 2010

I tried charging them off the car there was no option of changing the out put on the charger it was the charger itself that started smoking.
its a new charger so i guess it may have also been faulty.

anyway after that sago i went and bought a proper 6 volt charger charge both battery's even although they were showing almost fully charged on the charger.

i,l start from the beginning again, during the time it was laid up my father has been starting and leaving the car run till warm every couple of weeks, (news to me)

when i went to collect the car last week to bring it home went to start it engine turned once then the starter clicked a few time and then nothing hence be thinking the battery's were flat
no ignition light either
then as we stood there talking it just jumped into life on its own by this i mean the fuel pump started pumping and the ignition light came on
tried to start it and the same as before just died.
couple of minuets later it came back to life again so this time we bump started it and i drove it home the 30 miles.
after witch it was dead again.
witch lead me on to where i am now.
both battery's are showing charged but the cars still dead i guessing there's a lose wire somewhere but where to i start?
and keeping in mind the car was fine before being parked up last year.
s truman

Clean the battery connections first. Then, check the cable running from the battery to the starter, the beginning of your brown wire circuit. If the connections at the starter are not good, you have now power to the ignition or other circuits. If the connections are good, do a voltage check at the battery. Try to start the engine while reading voltage at the battery (either an assistant or jumper wires allow this to be accomplished) and see if the battery voltage drops when trying to start. If it does, battery or battery clamp problem. If not, and the car has not started, take a voltage reading at the main terminal of the starter while cranking. Any significant voltage drop indicates a bad cable from battery to starter--I have seen this happen twice.

As a side not, you mention the fuel pump coming back to life as you stood there. This would indicate the ignition switch was left on. Bad thing to do. If the points happen to be closed when this happens, you can burn up the wiring to and from the ignition switch.

Les Bengtson

Unfortunately a 6v charger on a 6v battery won't be any better than a 12v charger on both batteries in series.

If the ignition warning light suddenly went out with the ignition on but the engine not running, then came back on and the fuel pump burst into life, then there is a bad connection somewhere. This *could* be inside one of the batteries (but if the charger conencted directly to them shows fully charged then not), but could equally be any of the connections from battery to body (four), battery to battery (also four), battery to solenoid (yet another four), and solenoid through the ignition switch which could be a dozen or more connections! If the lights don't work either when the ignition light goes out this does eliminate the ignition switch and several connections, more likely to be down at the solenoid or further back towards the battery and battery earth on the body.

Incidentally whilst leaving the ignition switch on (with working electrics) is bad for the coil, and not good for the points, it won't burn up the wiring.

While you may think a witch has cast a spell on your electrics this is extremely unlikely, which only leaves something more straightforward.
Paul Hunt 2010

right then cheers for the replys i,l have a play about with the battery cables failing that then its a sparky.
s truman

right well had a play about and cant believe what i done when i refitted the battery's after charging them!

so back as the should be and the car is starting as normal so i think the original problem may have just been the broken battery clamp.
thanks for all the useful info on this thread
s truman

This thread was discussed between 17/04/2010 and 30/04/2010

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