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MG MGB Technical - Battery for MGB 1978

Hi guys,

I recently acquired a 1978 mgb roadster, 1800cc, and no later than 2 weeks the battery died ... not completely but it was discharged enough to not start the car. I checked the current drain when the car was switched off (by connecting a multimeter in series with the negative terminal) and it read 10mA. I assume this is normal ( possibly the clock). Checked the battery water level and it's ok.

I re-charged the battery and currently I am still waiting to see if it will discharge again but I am thinking of replacing it. Currently it has a Lucas Premium 3 - 60Ah - 600A cca battery installed. Is this battery appropriate for this vehicle ?

I am thinking of replacing it with a Bosch S5005 with similar specs... (63Ah & 610A cca). Would anyone advise against it ?

Thank you,
J Smith

The first thing, that you want to do, is to make sure that you need a new battery. I've seen too many batteries traded in because the owners couldn't get them to hold a charge. Most of the time, it turned out to be a fault in the charging system or a bad connection. When you have fully charged your battery, bring it to an auto parts store. Most of them have the equipment to test the battery while under load, simulating real life conditions. The battery must be fully charged when you test it, or you will get a false reading indicating that the battery is bad. RAY
rjm RAY

10mA seems high for a clock, but shouldn't be enough to kill the battery over 2 weeks. Mine has an alarm that when the battery was about a year old would flatten the battery over 2 weeks, and kill it within 2 years, but the current was quite a it higher than that. Fitting a battery cut-off switch to disconnect the alarm but keep the clock running has stopped the problem altogether.

Of course, with a car that is new to you the battery could well have suddenly failed shortly after purchase if you don't know how old it is and what treatment it has received, and there could be any number of problems with charging and drains.

As advised check charging before replacing the battery, with the engine running and the ignition warning light out (assuming it comes on when you first turn on the ignition!) you should get around 14.5v when the engine is revved. With lights, indicators and brakes on you should still get better than 12.8v at idle, although the cooling fan will pull it down a bit more. Any battery that properly fits the box and can be strapped down with the clamps is fine.

PaulH Solihull

This thread was discussed between 07/03/2011 and 11/03/2011

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