When fully charged, what voltage should a 6V NiMH battery read? I have a new pack that is not going above 5.6V.

What are you charging it with and for how long? How do you "know" it is fully charged? Can you measure the individual cell voltages? Do so if you can and see if you have a dead one.

Bruce,

Good questions, answers to which I should have already provided in my original posting, so here it goes:

I bought the pack some 3 months or so ago and didn't charge it when I received it. I am now charging it with a EOS0606i charger at a rate of 0.1A (the battery capacity is 2000mAh.) When I connected the battery 6 hours or so ago, the voltage reading was around 4.7 and it rose relatively quickly to over 5V but it is now stuck around 5.6V. I realize 6 hours is not enough at 0.1A, but I asked the question 1) for my education and 2) to be able to determine whether or not there is a problem with the pack.

Thanks.

By 6v do you mean a 4-cell pack??? In a perfect world a 4-cell Ni-MH pack would read 6 volts (1.5 volt/cell x 4 cells = 6 volts). Now in the real world the max voltage is going to depend a lot on the condition of the pack itself. If  it's truly fully charged it should read anywhere between 5.5 volts - 6 volts when it's removed from the charger.

Ken

No, I mean a 5-cell pack. Aren't NiMh batteries 1.2V per cell?

No, at a full charge (in a perfect world) they are 1.5 volts/ cell. So a 5-cell pack would (in a perfect world) be 7.5 volts at a full charge. In the real world you would probably get 7.0-7.5 volts fully charged. The 1.2 volt/cell you are talking about is the nominal voltage of the cell. Below 1.2 volts the cell needs to be recharged. Ni-MH packs have a discharge curve that quickly drops from fully charged to the nominal voltage of the pack where it will remain for approximately 80% of the battery life, then it will quickly drop off after that. So, for a 5-cell pack it will quickly drop from ~7.5 volts to the 6 volt level (1.2 volts/cell x 5-cell = 6 volts) where it will remain for quite some time (approximately 80% of the battery life), then it will quickly drop from their. So when you pack drops to 5.9 volts or less (measures with an extended scale voltmeter with ~300-500 MaH load) the pack should not be used any longer. Take a look at the attached graph to get an idea of the discharge curve for these batteries. (yes, it said Ni-cads but the discharge curve is similar for Ni-MHs)

If you have a battery cycler the best thing to do with a new pack is to run several charge/discharge cycles on it to determine it's initial capacity. On reason for doing this is for a baseline reading on the pack. Later in it's life when the capacity drops to 80% of it's initial baseline reading the pack should be taken out of service. The other reason for doing this is to get some idea of how much use you should get out of it at the field. This will give you a general idea of how long you can safely use the battery at the field. It'sa good idea to check the battery AFTER every flight with an extended scale voltmeter (ESV) to check it's capacity. Keep track of your flight time and you'll get a good idea of actual usage for that pack. But when it hits 5.9 volts or less time to recharge or quit flying.

Hope this helps

Ken