Hi Fishers Ghost
To answer your questions:
Firs lets go to this one:
You write: "OK so you take the 1.2 volt 1900mah batt and start discharging it into a load.at a rate of 1900 ma for one hour. At what point in time will it become 1.2 volt 1425 mah battery ? Will it be dead flat after one hour at 1900mah or does it still retain enough capacity to be able to deliver 1.2 volts at 1425mah? (Into a short cct maybe but not into a load like a metal detector) The terminal voltage of these batteries drops as the capacity is reduced during discharge and as this voltage drops so does the current delivering power into a load."
Example. You have a brand new 1900mAh battery. You are discharging at a rate of 1900mA. It will take 1 hour for the battery go flat.
At which point the 1900mAh batt becomes 1450mAh can not be predicted or calculated. You can calculate what it is at the moment by a known result. Your Infinium can work for only 10 hours before the voltage drops below 1.0V (considered flat). The Infinium draws constant 130mA.
Lets calculate: 130mA x 10hrs = 1300mAh. At this point after the length of time you've used these batts for, they have GRADUALLY become 1300mAh Up to this point of their capacity the voltage and current will be same as in a brand new battery.
Now, pay attention please.
As the battery gets older and number of times recharged grows higher, it's HOLDING CAPACITY gradually diminishes. The same battery might drop down to 1800mAh CAPACITY after one year, down to 1700mAh CAPACITY after the second year and so on. After it has reached its life limit, the capacity will be down to aproximately 1425mAh as above. This might take years! It depends how many recharge cycles it had.
It has nothing to do with any Voltage or Amperage! They will always have the same characteristics, only the battery will stay charged for 30% less time then it used to when it was brand new. It is exactly the same as if you go to the shop and buy a brand new NiMH battery at 1500mAh. You would have no questions about it's voltage or currents. You'll just paid a little less because its holding capacity is a bit less and it will stay charged for a little less time. As simple as that!
Another thing is, there is no such thing as a constant voltage or constant current battery. It cannot exist!
When on a FIXED load, the batterie's voltage drop goes down with the current drop. Let's say you are discharging a battery. Any battery. Rechargeable or not. The battery NiMH measures 1.25Volts. You hook it up tro a 10 Ohm resistor. By applying OHMS LAW the current drawn will be I = V/R , =1.25V/10Ohm = 0.125A or 125mA.
As the NiMh battery discharges it might drop to 1.2V after some time which will drop the current proportionally: I = V/R, = 1.2V/ 10Ohm = 0.12A or 120mA
When the battery Voltage drops to 1.0 V then the current becomes I=V/R, = 1.0V/10Ohm = 0.1A or 100mA and so on.
By now we have dropped from the initial 1.25V at 125mA to 1.0V at 100mA.
One more note on the batteries.
NiMH as well as NiCD batteries have a relatively flat discharge curve. Both of them, not just NiCD. Their nominal Voltage is lower than Alkalines, but stays put with only very little drop over the capacity of the battery. Then there is a sudden drop over the cliff and that's it.
Normal batteries and Alkalines are about 1.5 V per cell and start going down by tapering off the Voltage very slowly from the moment you put a load on them.
Now to your Infinium question. You have calculated it right! The batteries should comfortably power the Infinium for 17.7 hours. The reason they don't and go dead after just 10 hours is that the holding capacity of your batteries have OVER TIME diminshed from 2300mAh down to 1300mAh. This is a drop from 100% to about 56%. BTW, NiMH or NiCD under 1.0 Volt is considered flat. In other words, your batteries have aged, or were of doubtful quality when new, or have been always charged by a fast charger. They will still serve you, but go flat sooner. They're just not new anymore!
I hope I have been able to explain it clear enough.
Cheers
Jerry
I played around with some lipos that sat right under the control box.
fields.
...perhaps a nap is in order..