Re: Got 4Ah, not 5Ah, battery 18V (20V) - done right thing?

"Richard Smith"  wrote in message news:m11q60aggz.fsf@void.com...
Hi Clare, Jim, everyone.
These are DeWalt powertool batteries - 18V (20V?).
This characteristic you identify "1C" etc. becomes knowable?
Rich S
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On 5/16/24 I wrote:
"The C rating is the current the battery would provide for 1 hour before
falling to some minimum safe or useful voltage, though it's usually measured
at a lower current and longer time to get a more favorable higher number."
https://batteryuniversity.com/article/bu-402-what-is-c-rate
"To obtain a reasonably good capacity reading, manufacturers commonly rate alkaline and lead acid batteries at a very low 0.05C, or a 20-hour discharge."
The only satisfactory way to determine a battery's C capacity is to discharge it while recording the current and voltage, stopping when the voltage falls to the specified end point, which may be either where the battery may be damaged or the intended load will no longer function. Since this is slow, tedious and requires special equipment there are ways to estimate it, with varying accuracy. The professional way to measure it is with a programmable electronic load. The one I used to test large electric car batteries dumped its heat into a barrel of water.
At home I measure remaining battery capacity on the cheap with multimeters that can send their readings to a computer and either the device that the battery will operate or old surplus high power variable resistors as the load. The rotary type (rheostat) can be adjusted while hot to keep the power draw fairly constant as voltage decreases.
Using the device the battery will operate, typically refrigeration, tells me if the battery can be trusted to operate it overnight, which is more useful than the numerical Amp-hour capacity. An AC powered fridge draws a high startup current which can trip an inverter's low input voltage sensor although the battery could still provide the run current.
This and similar inexpensive devices can be wired into a stationary battery system to act as a 'fuel gauge' that shows the amount of current drawn and the voltage, from which you can determine when the battery has fully discharged and program the Amp-hour value in as C so the meter will then accurately(?) display the percentage of remaining charge. The fuel gauge Amp-hour reading halts at the full programmed capacity and ignores subsequent float charging current.
https://www.amazon.com/DROK-Multimeter-Charge-Discharge-Electricity-Overvoltage/dp/B01M5CWR2P/ref=cm_cr_arp_d_product_top?ie=UTF8
I set the Amp-hour capacity to the original rating and then can see the actual remaining Amp-hours and percentage of battery deterioration when its voltage falls near the full discharge level. The voltage rise when I switch off the load indicates the internal resistance, which increases with age. Separate calibrated meters connected directly to the battery terminals show its voltage regardless of IR drops in the load circuit, which affect the fuel gauge voltage reading.