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MG MGB Technical - NAPA Part # 24V Battery Early Car

Hi All,

Having resolved the '63's charging problems after 15 months of ownership, I now know that the batteries (two unknown-age six volts - but not original-size because they're too big for the tie-downs) are not holding the charge.

I see from archived posts that a single 12V replacement is a 26-series. Does anybody know the NAPA (USA) part number for the 26-series that will fit (I'm using NAPA because I have a business discount with our local store)?

Is it possible to get a 12V that can still be restrained by the stock tie-downs?

Thanks/Cheers,
Greg
Greg Van Hook

Sorry - thread title wrong. Stuck in 24V wheelchair battery land. I mean 12V.
Greg Van Hook

A little grepping around on the interweb seems to suggest that NAPA use the warranty and the group size together to form their battery part numbers. So a battery with an 84 month warranty in group size 26 would be part number 8426. I don't if an 8426 exists, but I'll bet whatever battery you end up with will have a part number of the form xx26....

HTH!
Rob Edwards

OK, a little education here. "26" = size?

I've seen "26E" and "26R", and maybe some others. But anything with a "26" will fit?
Greg Van Hook

Not sure what the 'E' suffix would be, but 'R' indicates that the positive and negative terminals are Reversed (relative to a plain 26). The group numbers are a standardisation of physical dimensions, as defined here:
http://www.rtpnet.org/teaa/bcigroup.html

So a group 26 is 8 3/16" x 6 13/16" x 7 3/4 (208mm x 173mm x 197mm) (L x W x H).

These dimensions don't seem to include any hold-down protrusions on the case. I've usually (but not always) had to trim those off, but that's easily done with a hacksaw or even a razor knife.

HTH!
Rob Edwards

That's a great chart! Thanks!

Just picked up my new 12V battery.
Greg Van Hook

OK, 12V battery installed, and the starter cranks over, I'd say, 30 to 50 percent faster, although the voltage at the batteries (new single 12V vs. 2 old 6V) at rest is approximately the same.

I guess the old batteries just couldn't handle the load - i.e., the solenoid (I installed a gear reduction started cuz the ring gear was worn where the old original starter engaged) wouldn't kick after the car sat a while.
Greg Van Hook

Doesn't compute. If the voltage was the same then the current and hence cranking speed would be the same. What you may have experienced is the removal of a bad connection at the battery posts, it depends on whether you measured right on the battery posts or the clamps. All MGBs had a solenoid, presumably you added a second one with the gear reduction starter, reducing the original to effectively a relay, no bad thing as it takes the load of the new solenoid off the ignition switch and wiring.
Paul Hunt 2010

I believe that the gear reduction starter, itself, has a lot to do with the increased cranking speed. The old inertia starters used a lot of juice to perform their task. RAY
rjm RAY

I still have the push-button solenoid up by the control box, which is bypassed now for the gear-reduction starter. But I've had that set up for months now. Still, with the new single 12V, the starter cranked MUCH faster.

I measured the 6V batteries after I removed them from the car. Something like 6.4V and 6.2V. I expected the voltage to be lower because I thought the batteries wouldn't hold a charge. I measured the new 12V on the posts all hooked up and ready to go, about 12.7V.
Greg Van Hook

When I bought my MGB, the previous owner had been having problems with the 6V batteries, the posts showed loads of hammer marks where the posts had been whacked with a blunt instrument. It turned out that the cable joining the batteries had been shorting out on the propshaft (driveshaft). 6V battery 1 was presumably overcharged most of the time and 6V battery 2 never saw much action and discharged what it had whenever it touched the propshaft.

This can't have been happening to you, Greg?

A single 12V battery solved all these problems.
Mike Standring

Open-circuit voltage is not indication of ability to *hold* a charge, just current (pun not intended) charge, and not very good at that. The correct way to test battery charge and capacity is with a load.

My roadster came to me with a single 12v battery and when that croaked I put twin 6v back in, with a new link cable. A few months later something made me remove the link cable, and I discovered the insulation had partly worn through from rubbing on the prop-shaft, so secured it up out of the way. Many years later I had to replace it as one connector was badly corroded and this time got the correct armoured cable, which I secured using the correct clip above the prop-shaft. However even that wasn't quite long enough, so I had to turn the right-hand battery round, which meant the 12v cable wouldn't reach. However I have a cut-off switch just inches from that battery, so used the good end of the old link cable to replace that. All a bit of a faff you might say, but I'll still stick with twin 6v while I can get them.
Paul Hunt 2010

This thread was discussed between 08/06/2010 and 14/06/2010

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