[sherelec]

I have had a T60 for about a week and was curious about the battery indicator because of some forum comments that I read before purchase. I have designed a few battery powered instruments so I have some battery knowledge and a Volt meter.

The Alkaline Duracell shipped with the unit was used until the player turned off (died) and measured 1.06V when removed from the player.

The 4 NiMH batteries I have used since have died at 1.03 to 1.07V, 2 run as Alkaline and 2 run as Rechargables. All started at about 1.45V.

Conclusion: the player shutoff is using a fixed Voltage Shutoff of approximately 1.05V, independent of the battery setting.

I have not tried to figure out which setting is more accurate for the NiMH batteries. But, from past experience designing equipment for both Alkalines and NiMH batteries, I note the following:

For Alkalines, a simple plot of output voltage versus time, at a constant current, will show a new battery at approximately 1.65V with a rather quick decay down to 1.55V then a linear decaying voltage to an end of life voltage (1.1 to 0.7V) depending on load. At the end there is often a short period of rapidly falling output, more pronounced at high load current.

The NiMH plotted the same as above will start out at 1.4 to 1.5V with very little initial decay. The voltage will look much more constant, over time, than the Alkaline. The end of life will be at a very fast rate, dropping several tenths of a volt over a few minutes. NiMH batteries do not like to be discharged much below 1.0V, as recharge cycles are much reduced.

The relatively flat voltage discharge for NiMH makes a voltage monitor state of charge indicator very difficult to implement. The Alkaline rather linear decay makes a voltage monitor an easy choice for a state of charge indicator. I am assuming that the T60 is using a voltage monitor to derive its state of charge display.

A good test would be to record the battery voltage where the bars change for both battery settings. However, I don't think that I am bored or patient enough to do that test!