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magictime

Batteries: nominal vs actual capacity when new

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Without getting into the specifics of my own requirements and/or experiences with batteries, or tangents about how batteries' capacity drops with time and misuse, or about how only half of a battery's capacity is really useable, etc., I'd be very interested to hear people's answers to this question:

 

In real-world use, how does the actual capacity of a brand new 12 volt  lead acid battery typically compare to its nominal or 'badge' capacity? Would you expect a battery badged at, say, 200Ah actually to provide 100Ah (or very close to it) before dropping to a 50% state of charge (if discharged at the appropriate rate, at the appropriate temperature, etc.)? Or is it generally the case that badged capacities are to be taken with a large pinch of salt and the real capacity can be expected to be X% lower?

 

 

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28 minutes ago, magictime said:

Without getting into the specifics of my own requirements and/or experiences with batteries, or tangents about how batteries' capacity drops with time and misuse, or about how only half of a battery's capacity is really useable, etc., I'd be very interested to hear people's answers to this question:

 

In real-world use, how does the actual capacity of a brand new 12 volt  lead acid battery typically compare to its nominal or 'badge' capacity? Would you expect a battery badged at, say, 200Ah actually to provide 100Ah (or very close to it) before dropping to a 50% state of charge (if discharged at the appropriate rate, at the appropriate temperature, etc.)? Or is it generally the case that badged capacities are to be taken with a large pinch of salt and the real capacity can be expected to be X% lower?

 

 

 

I have found that 'new out of the box' batteries will not offer full capacity, however, after a few 'training' cycles and ensuring they recharge to 99.99% they 'learn' and seem to offer close to the badged capacity - but it doesn't last long when real-life kicks in and they either get over discharged, or not regularly fully recharged.

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I'm fairly sure that some manufacturers make extensive use of a hefty "surface charge" to boost their claimed capacity figures.

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37 minutes ago, Keeping Up said:

I'm fairly sure that some manufacturers make extensive use of a hefty "surface charge" to boost their claimed capacity figures.

This exaggeration seems to be the case with Lead acid batteries, so I suppose it has created the rod for its own back..

 

However, where I have seen tests done on LiFePo4 batteries, (mostly by Will Prowse, admittedly), there seems to be a tendency for actual capacity to exceed claimed capacity.

 

I have always found it much nicer to sell something where buyers find they have got more than they expected, or, "It's so much better than I thought it would be", than to sell something where they have to make do, because that's as good as it gets.

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3 hours ago, magictime said:

Without getting into the specifics of my own requirements and/or experiences with batteries, or tangents about how batteries' capacity drops with time and misuse, or about how only half of a battery's capacity is really useable, etc., I'd be very interested to hear people's answers to this question:

 

In real-world use, how does the actual capacity of a brand new 12 volt  lead acid battery typically compare to its nominal or 'badge' capacity? Would you expect a battery badged at, say, 200Ah actually to provide 100Ah (or very close to it) before dropping to a 50% state of charge (if discharged at the appropriate rate, at the appropriate temperature, etc.)? Or is it generally the case that badged capacities are to be taken with a large pinch of salt and the real capacity can be expected to be X% lower?

 

 

For the most part when the battery has settled in a new one in my experience has the badged capacity or very near.  However, remember, how many amps one is drawing over time has a significant effect on amp hour capacity.  

 

The "C" rating is the hours the battery was (fully) discharged over to get the result 

 

A Trojan 12v 21XHS Battery for example rated at C5 (i.e. 5 hours to fully discharge) is 105AH at C10 120AH and at C20 130AH and finally at C100 144 AH.

 

The rating most often seen on websites is quoting the C20 capacity for the battery.  So if you have a higher avg draw normally you will find the battery discharges to 50% before the stated C20 AH capacity and if you have a normally lower avg draw the AH capacity will be more.

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I have some old and some newish 110Ah leisure batteries powering my leccy boat, all bought from low price ebay sellers.

 

I periodically perform a load test using a 55W headlamp bulb on each battery, checking the volts every few hours.  

 

most of the time I find I can draw off 50Ah before the resting voltage drops to 12.2v (this voltage is generally recognised as 60% of fully charged).

 

the conclusion is that batteries tend to have the capacity quoted.

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Thanks all. So it doesn't seem like there's any general perception that batteries' capacities are routinely overstated (to any great extent) by manufacturers. Hmm. Just wanted some more input really as someone whose opinion I generally respect was sharing his very negative view of this (that it's not uncommon for batteries to have maybe half the claimed capacity), but then I suspect he generally only finds himself dealing with batteries when they're either faulty or on their last legs, rather than just performing normally. 

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With lead acid batteries it is fairly well known that category and quality is often hyped way beyond reality.

 

Batteries with thin plates and high CCA are usual called  "leisure", and "deep cycle", when they are nothing of the sort.

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9 minutes ago, bizzard said:

Beware of the wording ''Heavy duty''.

 

My batteries weigh 53-55kgs each - its a real 'heavy duty' trying to wriggle into the engine room, on your back whilst balancing one of those on your belly.

I gave in with the last one and lifted the floor panels and lowered it into the battery box from above.

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On 18/10/2020 at 10:57, Alan de Enfield said:

 

I have found that 'new out of the box' batteries will not offer full capacity, however, after a few 'training' cycles and ensuring they recharge to 99.99% they 'learn' and seem to offer close to the badged capacity - but it doesn't last long when real-life kicks in and they either get over discharged, or not regularly fully recharged.

 

This ^^^^

 

It is because the active material is not fully formed when the lead acid battery is manufactured and the final forming takes place over the first few discharge/charge cycles.

 

As Churchward say, apparent capacity will vary with load. Heavy loads will reduce the apparent capacity. This is known as Peukert's Law.

 

https://en.m.wikipedia.org/wiki/Peukert's_law

 

Most leisure batteries have their capacity asseed at the 20 hour rate (C20), so at a constant 5 amps for a 100 amp hour battery.

 

Batteries for industrial use are usually specified at the 10 hour rate (C10).

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On 18/10/2020 at 10:26, magictime said:

 

 

In real-world use, how does the actual capacity of a brand new 12 volt  lead acid battery typically compare to its nominal or 'badge' capacity? Would you expect a battery badged at, say, 200Ah actually to provide 100Ah (or very close to it) before dropping to a 50% state of charge 

 

 

Yes

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