Battery capacity

[pmansson]

The E9 came with a 55Ah battery back in the early 70s. The CSL saved some weight by a measly 35Ah battery.
In one of my cars I put a 72Ah battery last year, which called for shaving off one of the short end`s protruding base in order to fit on the battery shelf.
What does the current expertise have to say with regards to battery capacity? One of my cars has a later style alternator with internal charge diodes. None of my cars have power consuming stereo/cellphone/extra headlights etc. 2 cars have Cibié headlamps with 100W bulbs.
Thanks in advance...

 

[jhjacobs]

If the battery cranks the engine vigorously when charged it is large enough. However, you need to make sure it can handle the coldest weather you will encounter. At -40C even a 55ah battery will have trouble. Extra power consuming stuff mostly impacts the alternator capacity.

Back when I was a student mechanic my boss (shop owner) always swore by dual batteries. He would install two smaller batteries and periodically switch them in and out; this way he always had a charged battery even if he left the lights on. Then again, he also monitored oil temperature and water pressure rather than the other way around; he said it gave a better picture of the operation status of the engine. Now that I think about it, he also ran dual fuel tanks. I think his Mercury station wagon was the most reliable vehicle on the planet and it had a 600 mile range.

 

[Honolulu]

batteries

Batts are sold by three numbers: Cold Cranking Amps, Reserve Capacity, and Cost.

If you live where it's cold part of the year, you want to look at CCA, which measures how many amps the batt delivers at a specified (cold, but I forget how cold), temp.

If you don't live where it gets cold, then CCA is largely irrelevant and you want to look at Reserve Capacity, which measures how many amps the batt can deliver before voltage drops by a specified amount. RC is the number to look for, if you live where it's warm, like me.

Cost... ah, well, the three major manufacturers have long ago figured out how long, on average, each particular size and construction will last. Then they price it just so that your batt will likely fail within the "warranty" period and you'll come back to claim your "warranty" (if you come back at all). But you paid that "warranty" up front, so they win if you don't claim it, and they win if you buy another batt from them.

Batteries have been commodity items for years now, and the battery industry has consolidated so that there are only three major batt makers left, selling under who knows how many brands.

So... I go to Costco, Walmart, Sams, whatever and get what fits. I check the electrolyte level from time to time, and replenish with tap water when needed. We have pretty good water here, you might not.

 

[pmansson]

Driven every now and again in 10deg C or warmer (about 50deg F or so) is 55, 62 or 62 Ah the battery to get??? Battery is under constant charge in between drives.