I finally died after 29570 seconds or 8.26 hours. At 584mA, 4821mAh. Seems the pack does meet their claimed 4500mAh but I just don't know how you would go about charging it with the scopemeter.
I wouldn't use any of the built in charging for the Ni-MH pack. I was thinking about this idea I had. Feel free to add to the idea or give feed back about it.
For charging a Ni-MH lack in the meter I was thinking about the following idea.
I would add a female micro/mini USB port that I can splice into the positive battery cage tab. Then using a power supply to supply power to a Ni-MH charging boar I can put it inline between the power supply and before the male USB plug. Maybe I can 3D print a bigger housing for the power supply and put the charge board inside this housing with a plastic wall for separation between the power supply and charging board.
Maybe start off with something like this one, or use one of the cheap chargers I don't trust that came with some LED flashlights and mod them?
http://www.ebay.com/itm/Ni-MH-Charger-Auto-Stop-Circuit-board-1-to-10-cell-800mA-MJE2955T-12-16VDC/140353600313?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D38530%26meid%3D302ca39224134343948c276a38f87bf0%26pid%3D100033%26rk%3D2%26rkt%3D8%26sd%3D401046168634I would wire it so when the USB port is plugged in it will disconnects the positive line from the battery packs to the meter preventing the meter from running off the battery when it's charging. Then provide the positive line from the charging board to the battery positive terminal, not the charging tab. I would disconnect the wire from the onboard charger to the battery cage. This way you can also plug in the stock power supply to run the meter at the same time it's charging the battery from the USB port. This will also allow standard Ni-MH C cells to be used without a need for a charging tab and could charge them from the USB port. Also running standard C cells will be easier to check the individual cell voltage and replace a bad cell if one dies.
Interference from the charging board should be minimal since the charging circuit will be external and away from the meter with at least 3 feet of wire or longer.
The charging board would have an adjustable charge current controlled by a resistor pod. I can use a in line USB power monitor for adjusting the current so I won't need to put a display on the charging board. My USB power monitors from YZXStudio runs from 4V to 14V with little burden voltage and little power consumption.
My concerns would be the charge rate and the heat generated on the cells as they increase to full charge capacity in that little battery compartment that is sealed with an O ring. I can use the USB data lines to a K style thermostat or thermistor that I can hot glue the sensor inside the battery compartment. Then include a temperature cut off monitor on the charging board when it reaches a set temperature. I did read about a Ni-MH charging method that was based off the temperature only. The charger turns off when it hits a set temperature despite the voltage levels. This charging style is new to me so I would need to research it but it makes sense. I would also want voltage monitoring as a backup cutoff.
If the pack doesn't get too hot when charging then I can set the charge board to put out 1A or maybe higher for a faster charge. NI-MH batteries are designed to charge with higher current and they could over charge with low current like from the built in Ni-CD charger. The built in charger won't be able to detect when the cells are full when it's doing a trickle charge that would over charge the NI-MH cells.
I will probably just disable any trickle charging on the Ni-MH board so it might drop the total capacity when it's done charging the pack, but not much loss difference in capacity. It will still have plenty of capacity for long run times and shorten the charging time a little. This way the Ni-MH pack would charge faster with temp cut off as the cell fills up to near full capacity as they reach near full charge.
TIP:
I soldered a pin to the end of an old probe (or you can solder it to the wire with a male bandanna on the other end) and poked little holes in my pack so I can check the individual cell voltages without unwrapping the pack. I wouldn't recommend using this pin probe for LiPo packs since they are easier to puncture.
So far mine seem fairly balanced, well within spec for what I would expect from a Ni-MH pack without balancing capabilities. A little trick I used to do with RC packs to check for a bad cell without having to unwrap the pack. I used to charge the packs at max current. Heck the old Ni-Cd packs we used to charge them in a ziplock bag then put into an ice cooler so they would take the max capacity and have a longer run time. It killed the packs faster as expected, but it was racing so competition brings out inventive ways to win within the rules.
I know my charger is a delta charger, so I can set the mV for the trickle to top it off or leave it on automatic. This was an idea to top off all the cells to the same level. Not sure if or how it really works. I just kept it on automatic. I changed over to LiPo packs shortly after this and stepped into the next class of races.
Thank you,
Scott