Dodgy battery

[Ignatzcatz]

The battery in my 356 is of unknown origin, I can't recall where or when it came into my possession but it got fitted into the car when I started re-wiring it. It's never been good, always needed re charging and this weekend bloody thing let me down just when I wanted to go out. So out it went and I do have a very good slave battery which I thought I might use in it's place. The only thing is the old knackered one was 38 amps and the new, good battery if 70 amps. I run an alternator and 12volts but I'm just wondering if the 70amp spec is OK for the car or could this rating be too much. Electrical experts please advise.

[davep]

That sort of depends on the Amp rating that you are speaking of. If it is the capacity rating such as Amp-hours, then the 38 was well on the low side, and the 70 is just about correct. However, usually batteries that are rated in Amp-hours are designed for a completely different purpose than automobiles. Such batteries are designed to power equipment at low amp loads for long periods. For example, the 38 Amp-hour rating is calculated at a 20 hour period of 1.9 amps current draw. So obviously not the 200 amp draw of a starter motor; they are not designed for high amp bursts like an automotive battery. My suggestion is to get a proper automotive battery designed for the purpose.

[roy mawbey]

Yes agree with above, the batteries should be 70 Amp/hour or above. The correct number should be 77 that was previously 84 as stated in my manual. Think they changed the numbers a long time ago.
Your 35 figure is as stated really low.

Interesting though why ampere hour factors come into play.

My last battery a NOMAX 404 sits well in the tray and is soon to be 5 years old still working well with the Accumate conditioner always used. It cost me then about £120- which was I thought a huge uplift from years ago. I bought it from Milestones the tyre and battery chain. But it was a 6 volt !

Roy

[Ignatzcatz]

The old 38 amp battery was an agricultural fitment which meant it must have come from my mates farm where he always uses things right up to the point when the item is completely void of any life, then he palms it off to me. However the 70 amp seems to be working well and I shall keep it until I get an Optima battery which is what I had in my US pick-up and it gave me no trouble whatsoever even after having the CD player blasting out all day, it still started the big V8 no problem. These Optima are big in the states but it seems the only supplier is a mob up in darkest Welsh Wales. However I shall have one in due course.