Boost voltage

[BartDB]

(06-08-2015 11:39 PM)Claudio L. Wrote:  The NiMH batteries read 1.18 V without load, ...

Yes, even depleted batteries will show a no-load voltage close to their normal operating voltage (there is still a small amount of active material in the electrodes, and the electrode potential always remains the same, it is the internal resistance that causes voltage drop and this only happens when a current is flowing. The internal resistance of a depleted battery is higher than that of a charged battery hence the voltage drops more for a depleted battery (there is less active material available in the electrodes thus increasing resistance)).

However, as soon as you put a load on them they "collapse" quickly as you have shown.

(06-08-2015 11:39 PM)Claudio L. Wrote:  I put the batteries back and the calculator is functioning, so it looks like they bounced back after the reset loop. But with the critical warning on, under load I'm getting 4.21V (slow mode). I started calculations, and voltage dropped to 4.10V. It stayed there for 10 seconds, while the machine kept doing calculations in a tight loop. After that, started descending slowly (around 0.1V per second) and it went downhill from there all the way to 3.5V and started resetting.

So it seems 4.10V is still not as safe as my previous measurements would suggest (this probably is an older set of batteries, with many recharge cycles on them). I'll have to revise my numbers.

You are basing your final statement on re-inserting using batteries that are already depleted. This is nugatory. You need to log the voltage of a charged set of batteries from start to finish to see how the voltage drops over time and base your decisions on that.

My personal view is that your settings seem perfect:
1) a few hours once indicator comes on = will probably last to the end of the day giving enough time to get home and put in charged batteries.
2) "critical indication" in my mind would = replace now, so an hour of operation seems acceptable.

Best regards.