We also used deep cycle ones for other uses - and they were run flat every time. Didn't last a year at full capacity. And they did nothing like the number of cycles I'm talking about. Basically deep discharge and lead acid don't mix.
Then why bother measuring it if you already knew? Determining the answer before you even started is not a good way to do things.
There is no easy way without knowing the acid concentration, and the temperature and the plate chemistry of determining state of charge from terminal voltage. It simply cannot be done - you can tell if it's just come off charge, or if it's flat but that is all you can reliably do.
No you said about one that you didnt check properly and without stating the plate chemistry or construction method. There is a huge difference. After spending a lot of time in a lab doing reseach on this I can assure you that 60% a month is not at all unusual, and one reason that people are moving from straigh lead acids to better ones that don't self discharge to the same extent.
Essentially yes. A pasted plate car battery delivers a huge current as it has a large surface area, but the plates cannot take long term abuse and easily shed material, grow dendrites, short out, buckle and warp etc. A car battery is built to deliver massive currents, and the capacity is a side effect of this requirement. Deep discharge are built to deliver capacity, not current and the two are somewhat of a comprimise. Service life also comes into the design considerations, some forklift batterys can take 50% discharge daily none stop for a decade or two, but the capacity is minimal compared to a car battery - maybe only
10% of the capacity in a given volume and weight.
I'd suggest you look at some of the electronic testers available these days. They give pretty accurate results instantly.
Dunno what you mean by a 'straight lead acid'. There have been subtle changes in car battery designs going on for many a year.
Yup, don't discharge them in less than 4 hours & charge them in 4 to 8 ideally. Discharging them in an hour gives you les capacity, but doesn't damage them the way hard discharging a car battery does & if you shop you can get the same Ah (although way less CCA) for the same money. But if you're looking for repeated sub 1 hr discharges & recharges then you want Nicds
10% of the CCA, you should get rather similar nominal capacity for the same weight & volume.
Well running them to dead flat kills them, for the same weight, volume & price a deep discharge gives you more capacity so you don't have to dead flat it. Abuse anything & it'll be uneconomic in the long run.
Have you ever checked the accuravcy? If I couldn't find it accuratly in a lab with a temperature regulated cell, and a standardised voltage reference and 30ppm meter what chance do you think a bung it on the terminals and guess meter is going to have? It's a bit better than a wild ass guess and that's about all you can say.
For a true long life battery no... the plates will ahve considerably more lead in for the same surface area (unless it's one of the really new carbon fibre reinforced ones) and the plates are a solid construction often which means less surface area from a sponge-lead pasted plate SLI battery...
Lead antimony alloyed plates with a positive grid non passivated with calcium or silver and a 30% sulphuric acid electrolyte formed with 140% at first use maintained at 298K with a bubble stirred system and discharged out unto a standard C/20 load after a month standing.
ie - a common duty cycle for a common car battery up to about 15 years ago.
Which is why I chose to use larger than needed batteries if possible. Something which will do a full day without going beyond about half discharge. But I'm not sure where you get deep discharge ones for a lower price than a same capacity car one.
Sadly in my job you can't stop people 'abusing' batteries. So you have to take steps to prevent it happening where possible.
I have discharged a battery at the correct rate and its actual capacity tied in well with what the meter said. Which at the end of the day is mainly what's needed on a test.
Weirdly the last non-gel one I bought came from the local car shop, but forlift truck suppliers are generally the cheapest.
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