TA Battery Replacement

[Phil Dadd]

For those who do not kinow, the TA is fitted with two 6 volt batteries which when joined = 12 volts. They are situated at the rear of the car, under the tonneau box, on either side to give balance.
Some years ago, when the batteries failed it took me over a month to find replacements, so I decided to install a single 12 volt unit. This was over 10 years ago and has worked perfectly. When the battery needed replacing it was an easy task to purchase another one. I did leave one of the 6 volt units in place to give weight balance to the rear of the car, This had the cables removed.
I have recently rebuilt the engine and find that there is not enough power in the existing battery to start the car. If I use jumper leads, it fires up immediately. Because of the ease of finding and replacing a 12 volt battery when and if necessary, I would prefer to stay with using 12 volt batteries.
Auto electrics are to me like some ancient and completely indecipherable language, so please humour me if what I am to say sounds ridiculous. The original 6 volt batteries are CCA270. I am assuming that when joined this will equal a CCA of 540 which is the same as that in my modern car. The single 12 volt battery currently in the TA is CCA325 and does not have sufficient power to turn the engine fast enough. When combined with that of my modern car it gives ample power and the car starts.
I am assuming that because I have never had this problem before, it is because the engine was well run in and much freer than this rebuilt one.The "new" engine is too tight for the available battery power. If I buy a second CCA325 battery and run this in parallel with the original, will this give me a combined CCA of 540 and sufficient power to start the car? If yes ! will running these two batteries together cause any problems with the other electrical components e.g light bulbs etc? Should I run them in Series or Parallel?
The reason for thinking to buy a second battery is to give a weight balance in the rear of the car. A single more powerful battery may be too large to fit into the space available.
Any thoughts?
Phil Dadd TA 2982

[Steve Simmons]

My first thought is that removing the "extra" battery will do more for performance through weight loss than leaving it there would do through balance. If you're worried about balance, then do like the MGB guys do and put the battery on the passenger side, because as soon as you sit in the car you're putting ten batteries worth of weight on one side. And that's assuming that the car is balanced left to right before the batteries are installed!

As for required power, I don't believe a newly rebuilt engine would (or should) ever have enough friction to prevent the starter from turning it easily. More likely your battery is failing or there is an electrical fault in the system. I ran a big Optima battery in my TC for over a decade, and when it died I replaced it with a Westco battery as used in the first generation Mazda MX-5. I've run these batteries in several other MGs with great success. In the TC, it cranks the engine just as fast as the giant Optima ever did. I recommend a single 12-volt lightweight AGM battery for your car.

[frenchblatter]

Get a Lithium-ion battery. Pick it up with one finger, about the size of a bag of sugar and enough power to turn my 11:1 CR Cosworth engine over for a few minutes.

I goy mine for about £100, if you shop around you should find one that's not silly money (like £500 from DT in the UK)

[mgtamike]

It might be worth checking the switch on the starter.
A small resistance here combined with the very large current gives a big volt drop.
Its not helpful that you can't get to the starter motor to measure the voltage applied to it. You should first check the volts at the starter switch terminal when cranking the engine. If it drops significantly at that point you should be checking battery, connections and wiring. If that's all Ok then you could remove the switch (3 small bolts) and check and clean the contacts.
My TA has run on a single battery for 15 years or so. I don't think you will gain anything from another battery.
Hope this helps, no guarantee this time.

Mike
PS If you put two 12v batteries in series you get a 24 volt supply. The starter operation will be fantastic and all the lights, wiper motor, horn etc will burn out immediately they are turned on, the dynamo will try to generate 24v and probably fail.... not a good plan!!

[Gene Gillam]

Phil...

Check your battery connections...ensure they're clean and that the cables are tight and not frayed - in addition to checking the starter switch. It sounds as if you've got a voltage drop somewhere in the system.

You can always buy another 12V battery and wire it in parallel with the existing one - same 12V output but double the current (which is what spins the motor).

This is what I use - tiny size:

[mgtamike]

Err. You won't get double the current.

Have you refitted the gearbox to frame earth strap, and are the connections clean and tight?

[Chris C]

I agree with the previous suggestions - most likely is high resistance joint between the battery and starter motor or a failed battery (was it left untouched and unrecharged while you rebuilt the engine)

I use a Bosch type 063 12v battery with a tool box on the other side, far more use that a dead 6v battery!

The two original batteries in series would only deliver a cold cranking current of 270, any modern battery would be better that that.

Finally not a good idea to put lead acid batteries in parallel, any slight imbalance will lead to large currents flowing from one battery to the other.

Almost certainly all you need is a new battery.

[Gene Gillam]

mgtamike - you're correct - I meant double the current capacity, i.e., the drain on your batteries will be halved (shared across both instead of one).