morganj

For 1600mAh NiMH I would say 10 - 11 hours. See also http://opentopic.Groundspeak.com/0/OpenTopic?a=tpc&s=1750973553&f=5740990093&m=2530963834&r=5320918934#5320918934 and http://opentopic.Groundspeak.com/0/OpenTopic?a=tpc&s=1750973553&f=5740990093&m=4910905034 "Qui quairit invenit" /Morgan Geocacher and MinuteWarrior

I have made some measurements of battery life with an eTrex Venture, see http://opentopic.Groundspeak.com/0/OpenTopic?a=tpc&s=1750973553&f=5740990093&m=4910905034 I also want to share what I have learned about the capacity and voltage ratings for alkalines and NiMh The 1,5V in alkalines and the 1,2V in NiMh is not comparable. For alkalines 1,5 volts is the open-circuit voltage (The no load voltage of a cell or battery measured with a high resistance voltmeter), that means no current drain. That is not the whole truth, an unused alkaline has a open-circuit voltage of 1,6V but that soon drops to 1,5V. If you measure the open-circuit voltage on a fully charged NiMh directly off the charger the open-circuit voltage is almost 1,4V. The open-circuit voltage is the above 1,2V until it's discharged. But we have no use of the open-circuit voltage. We use the batteries to power all out gadgets. If you plot the closed-circuit voltage (Voltage as measured of a cell or battery under a specific discharge load and time interval) versus discharge time there are big differences. This discharge characteristics are very different for alkalines and NiMh. I found some illustrative diagrams on Energizers website. Take a look at http://data.energizer.com/datasheets/library/primary/alkaline/energizer/consumer_oem/e91.pdf for alkalines and http://data.energizer.com/datasheets/library/rechargeables/consumer/nimh/nh15.pdf for NiMh. The first thing to observe is that the rated capacity is defined at different rating drain. The NiMh is rated to 1700mAh at 340mA current drain and 1.0V cut off, the alkalines to 2850mAh at 25mA current drain and 0.8V cut off. The capacity for the alkalines at 340mA current drain and 1.0V cut off is only 1350 mAh (from the diagram "Constant Current Discharge Typical Service). The eTrex shuts down at 2.0V, that is 1.0V/battery. The next thing is that the discharge diagrams looks different. For the NiMh the closed-circuit voltage drops to just below 1,3V and thea stays there to the end of the discharge when it drops fast. (at 170mA current drain, close to an eTrex). 1,2V closed-circuit voltage is not reached until after 90% of the capacity is used. For the alkalines 1.3V is reached after 15% and 1,2V closed-circuit voltage is reached after 50% (according to the diagram "3,9 ohm 1 hour / day" and 1,0V cut off) of the capacity is used. This means that during most of the time the NiMh has a higher closed-circuit voltage than the alkalines! This is why the NiMh works so good in our GPSr's despite the 1.2V rating. In low temperatuers it gets even worse for the alkalines. All this is also consistent with the results of my own measurements. The discharge diagrams also explains the behaviour of the battery indicator in the eTrex (and others I believe). "Qui quairit invenit" /Morgan Geocacher and MinuteWarrior

Yes, profiles like this is on top of my wish list for the eTrex Venture too. Maybe we should send one email each to Garmin. "Qui quairit invenit" /Morgan Geocacher and MinuteWarrior

There are lots of discussions about batteries and battery life in GPSr, and lots of different opinions. But I have newer found any real measurements except for those at Joe Mehaffey. So a couple of months ago I decided to do some measurements my self especially in low temperatures. I'd like to share my observations . I have used a Garmin eTrex Venture. I set up the tracklog on time and interval to 1 minute. I put the eTrex on my balcony during the measurements with half the sky blocked by the building. This caused the GPSr to lose contact for 1 –2 minutes a couple of times during each test. The procedure was, put fresh/charged batteried in the GPSr, switch on, clear the track log, put it on the balcony. It stayed there until it switched of itself. The track log was transferred to OziExplorer and the time was calculated as the difference between the last and the first track point. I have used three different batteries, cheap nobrand alkaline (bought at IKEA, the furniture store) 24SKr ($2.4) for 10, high quality alkaline Duracell M3 55Skr ($5.5) for 4 and NiMh GP 1600mAh. The measurements where made at ambient temperatures about 0°C (32°F) and about -10°C (14°F). Some measurements was made with power saver on. No backlight was used. Some measurement was repeated a couple of times others not. That means that the statistical basis is non existing. So don't take this as a scientific truth but more like a hint on the differences in moderate low temperatures. For alkalines the full capacity is not available in one single discharge at the current load in a Venture, something like 150 mA. If I let them "rest" for 12 hours after the first discharge they are useful for another 1-3 hours. In the comparison here I show the time for the first discharge because for me that's the most relevant, I usually use the GPSr for 5-10 hours at a time. Others may have a different opinion. Summary of battery measurements. Hours of continues use Battery 0°C -10°C 0°C+ps -10°C+ps IKEA alk 5.5 4 9.5 4 Duracell alk 9.5 GP NiMh 10.5 10.5 13 The conclusions I come to are that nobrand alkalines have a limited capacity in low temperatures. High quality alkalines have capacity comparable to NiMh at least at 0°C but at significant higher cost/hour. You also get a higher percentage of total capacity in the first discharge. NiMh capacity is not degraded from 0°C to -10°C. Power Save mode gives you about 30% longer time but the current data are inconclusive. I consider NiMh the best choise for me for the moment . In Joe Mehaffey's test alkalines had slightly higher capacity compared to NiMh. I think there is two reasons for that. First I have tested at lower temperatures (I think, hi don't specify ambient temperature) and second the Venture has about double current load (due to 2 batteries instead of 4). And the higher the current the lower the available capacity for the first discharge. I have also tested Alkaline rechargeable batteries but they are no better than ordinary alkalines when they where new at low temperatures and the capacity degraded after recharging just 5 or 10 times. I don't consider those useful to me and didn't include them in this test . I plan to make more measurements this summer at 20°C (68°F) and next winter I'll fill in the blanks in the above table and also measure at -20°C (-4°F) including lithiums. I'll be back with these results. What are your own experiences? "Qui quairit invenit" /Morgan Geocacher and MinuteWarrior

There are lots of discussions about batteries and battery life in GPSr, and lots of different opinions. But I have newer found any real measurements except for those at Joe Mehaffey. So a couple of months ago I decided to do some measurements my self especially in low temperatures. I'd like to share my observations . I have used a Garmin eTrex Venture. I set up the tracklog on time and interval to 1 minute. I put the eTrex on my balcony during the measurements with half the sky blocked by the building. This caused the GPSr to lose contact for 1 –2 minutes a couple of times during each test. The procedure was, put fresh/charged batteried in the GPSr, switch on, clear the track log, put it on the balcony. It stayed there until it switched of itself. The track log was transferred to OziExplorer and the time was calculated as the difference between the last and the first track point. I have used three different batteries, cheap nobrand alkaline (bought at IKEA, the furniture store) 24SKr ($2.4) for 10, high quality alkaline Duracell M3 55Skr ($5.5) for 4 and NiMh GP 1600mAh. The measurements where made at ambient temperatures about 0°C (32°F) and about -10°C (14°F). Some measurements was made with power saver on. No backlight was used. Some measurement was repeated a couple of times others not. That means that the statistical basis is non existing. So don't take this as a scientific truth but more like a hint on the differences in moderate low temperatures. For alkalines the full capacity is not available in one single discharge at the current load in a Venture, something like 150 mA. If I let them "rest" for 12 hours after the first discharge they are useful for another 1-3 hours. In the comparison here I show the time for the first discharge because for me that's the most relevant, I usually use the GPSr for 5-10 hours at a time. Others may have a different opinion. Summary of battery measurements. Hours of continues use Battery 0°C -10°C 0°C+ps -10°C+ps IKEA alk 5.5 4 9.5 4 Duracell alk 9.5 GP NiMh 10.5 10.5 13 The conclusions I come to are that nobrand alkalines have a limited capacity in low temperatures. High quality alkalines have capacity comparable to NiMh at least at 0°C but at significant higher cost/hour. You also get a higher percentage of total capacity in the first discharge. NiMh capacity is not degraded from 0°C to -10°C. Power Save mode gives you about 30% longer time but the current data are inconclusive. I consider NiMh the best choise for me for the moment . In Joe Mehaffey's test alkalines had slightly higher capacity compared to NiMh. I think there is two reasons for that. First I have tested at lower temperatures (I think, hi don't specify ambient temperature) and second the Venture has about double current load (due to 2 batteries instead of 4). And the higher the current the lower the available capacity for the first discharge. I have also tested Alkaline rechargeable batteries but they are no better than ordinary alkalines when they where new at low temperatures and the capacity degraded after recharging just 5 or 10 times. I don't consider those useful to me and didn't include them in this test . I plan to make more measurements this summer at 20°C (68°F) and next winter I'll fill in the blanks in the above table and also measure at -20°C (-4°F) including lithiums. I'll be back with these results. What are your own experiences? "Qui quairit invenit" /Morgan Geocacher and MinuteWarrior