Drop testing a new battery

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Matata

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Reading in the latest comic discharging a lead acid battery at say 10 amps you should get 80% of the stated capacity of the battery with a cut off point of 10.5v. Ive made a test rig and discharged a few batteries through a car bulb at a constant 5 amps. Im struggling to get 70% of the stated capacity. I have charged the batteries with a ctek good quality charger and they do reach the float setting. any comments or ideas? As a separate note my ford focus battery must be replaced with a calcium lead battery as it accepts a higher charging voltage. A ford alternator apparently charges to a higher voltage. Thoughts??? Be strong Nik
 
Your findings would corelate to my expectations. For a variety of cumulative reasons battery size AH claims are no possible to reproduce in practice. good luck olewill
 
The discharge rate has a strong influence on the capacity of a lead acid battery.
What size is the batery?
If you want to compare the measured capacity against the stated nominal capacity the discharge rate has to match the discharge rate used when the battery capacity is specified.

A 100% SOC is difficult to achieve and typically needs a long time on float.
 
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You don't say what type of batteries you are doing this with but, unless they are true deep-cycle batteries then taking them down to 20% or 30% is probably overdoing it and you may well damage the batteries. Most people seem to recommend just taking them down to 50%.
 
BruceDanforth said:
I was reading somewhere the stated capacity was worked out based on a discharge time of 20 or maybe even 100 hours in some cases. Are you going too fast?
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Usually, but not always, the capacity is quoted at the 20 hour rate. Unless the Op has a vey large battery 10amps will be too high and will give a low apparent capacity value. 5amps would be closer to the correct rate
 
Good advice above. Temperature will also have a bearing, with efficiency only around 50% at 0C, reaching 100% at around 25C.
As suggested, a normal capacity test would take the battery down to only 50% discharge (as measured with a hydrometer), and the nominal 100% worked out from there. A healthy battery should show something like the manufacturer's claim, providing it truly was fully charged to begin with and was discharged at the appropriate rate.
 
The only time I, inadvertently, did a drop test on a battery, it smashed onto the concrete, and all the acid fell out.:disgust:
 
Thanks for all the replies. my lead acid battery is stated as 100amp hr. I was discharging at 5amp which is c/20. I measured the current and voltage and the current remained remarkable constant at 5.15 amp to start and finished at 4.85 amp. therefore 5amp /hr is a good guide through a car headlamp bulb. All at room temperature. Bearing in mind its very difficult to charge up beyond 80% and running a battery below 50% is generally not a good idea , I'm beginning to think there is not as much usable " whack' in a battery as I first thought! Maybe no more than a safe useable 30 amps.Anyone any recommendations for a good rugged 100amp /hr lead battery around £100 leisure or traction or are they much the same? Regards Nik
 
Matata said:
Im struggling to get 70% of the stated capacity.
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With a new battery you have to charge and discharge it 20-30 times before it will deliver full Ah capacity. Never discharge below 50%, or about 12.2v UNDER NO LOAD and after resting for 6 hours.

Matata said:
...I have charged the batteries with a ctek good quality charger and they do reach the float setting.
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Float setting doesn't mean you are at 100% State of Charge - maybe only 85-90%. Leave it at least another 12 hours on float to get anywhere near 100% SoC.
 
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