Originally Posted by Paul L
I'm not questioning what you are saying, I'm interested in a little more detail. If you fully charge a battery, and then leave it without load for multiple hours and then read the standing voltage, doesn't this give you a reasonable measure of the batteries health
? If the spec says 12.95 is max and you read 12.8, then the batt is somewhat depleted (say 10-12%), etc.
Of course if you measure the voltage of the battery and it reads 12.8 then 99% of the time the battery will be ok but it in no way indicates the state of health of the battery.
I remember the AGM
battery I had a few years ago and it read well over 12V after leaving it standing for more than 24 hours after charging
. But when a tiny load was connected (even a 12V light globe) the voltage would instantly drop to 2V and the battery would completely die. The "surface voltage" reading of 12V can be very misleading and is in no way is a reliable factor in determining the condition of a battery.
The only reliable/accurate methods of testing a battery for its age and state of health are a load test and impedance test. Since the impedance (internal resistance) of a battery increases as it ages it is easy to compare this reading with the internal impedance of a new battery to determine how closely it will perform to a brand new battery.
cells are impedance matched to make racing
batteries since each cell in the pack will have virtually identical performance in terms of charging
and discharging performance. Cells can be measured and the best cells used to make a battery which will provide the greatest discharge power.
Of course this is not so important for cruising boat owners but is used for racing
For example below is a photo
cells being assembled into battery packs fitted in a custom fiberglass
case. The little yellow label stuck on the cells has written on it the actual measured impedance of the cell thereby allowing the batteries to be assembled using cells with the same performance characteristics. The battery pictured is used to power the world's most powerful/fastest electric
powered bicycle which is built in Europe