lostinthewoods

Did I miss something or did someone else? As of May 18, 2006, garmin's download site for the GPS60 firmware says: Changes made from version 2.30 to 2.40: * Improve WAAS functionality. * Add capability to support NMEA over USB. So, maybe yes?

But then it's not over one spot on the globe at all time, hence not 'geosynchronous'. Yes, it'll have a constant longitude, but varying latitude. Bonus homework. Okay, so you can incline the orbit of a longitudinaly synchronous satallite, but *how* much? I.e. What happens when you incline the orbit by 90 degrees? Orbital mechanics is a good way to end up grabbing the sides of your head and yelling 'oww owww oww'.

I see only one possibly thing that can reconcile out differences. That is the fact that operating at higher temperatures will increase the internal cell resistance and result in lower *apparent* cell capacity. Thus, each charge/discharge cycle results in fewer minutes of use--worse for higher discharge devices than for low discharge ones. This means that in, say, 6 months of continuous use, the cells in the hot environment will have been cycled more times than those in the cold environment. Thus, the hot environment cells will hit their cyclic charge limit sooner than those used in the cold environment. Does this agree with you?

I have some of the orginal 2000mAh Ray-O-Vac cells and the 15 minute charger for them from two and a half years ago. I use them fairly regularly and they've performed better than any other rechargable batteries I've ever had. If they were cheaper, I'd own more. A good companion is the Ray-O-Vac 60 minute charger--Radio Shack may sell a rebrand of that as well, I'm not sure. The 60 minute charger does a good job on any cell that will fit into it--in about an hour.

I've not heard of this, before. I can do some research and see what I come up with, though. The temperature of a cell is directly related to it's self discharge rate, but that only discharges a cell, it does no long term damage. If you were to charge a cell in a nice cool room, take it out in the mid-day sun in the desert and put it in a black box, it would discharge quite quickly--cell phones in hot cars have been reported to run down in a day. But, if you took it back into the cool room, you could recharge it and it would be in as good of condition as a cell which had been discharged in the cool room. All of that is assuming you don't take the cell temp into the 'boil off' temperature range of the cell. If you do that, you can kill *any* kind of cell which has electrolyte in it. Because, hey, it's a liquid, it'll boil at some point. And, once it's gone, yeah, the cell won't work any more. Is that what you meant?

You are completely correct. Slipped my mind. Good catch.

GPSMAP60Cx manual page 74 says expected battery life is 18 hours. While for the 60C it's 30 and the 60, it's 28.

Nerys, What you say about 15 minute cells is partially right if you will include a caviat. That being they are not the Ray-O-Vac 15 minute style of cells. They have a 'switch' inside them that opens when the gas pressure builds up. And, it's a bit simplistic to say that heat is what kills NiMH cells. You need to know the source of the heat to fully explain the issue. There are three main sources of heat in the charging of a NiMH cell: 1) resistive losses in the cell 2) the charging reaction is exothermic--it releases heat (NiCd charging is endothermic--they actually suck in heat when they charge) 3) Heat given off by the recombination of oxygen and hydrogen that is electrolysed out of the water in the cell after the cell is fully charged The first point is going to get worse with higher charge currents, but with modern cell design isn't really a factor until you get to *very* high currents, so we can mostly ignore it. The second point isn't particularly large--the amount of heat released by the reaction isn't very great. The first two points together *do* cause a noticable increase in cell temperature as it charges--and many good chargers monitor this as a 'state of charge' indicator. The last point is the real killer as it causes two problems. One, if the cell is an older NiMH (probably around the 1600mAh generation of domestic cells, possibly up to 1800mAh for asian cells) design, they lack the ability to recombine the gasses quickly enough to tolerate much overcharge. Such cells may burst if overcharged. Newer cells have a much more agressive catalyst system for recombining H2 and O2. *But*, that just means they convert all overcharge energy into heat--but at least they don't explode! The Ray-O-Vac cells address point 3 with their internal pressure switch. So, with the Ray-O-Vac 15 minute system, there is no reason for them not to have a nice long life. As I said in a different post, I don't know if the Duracell 15 minute system is similar. It very well may be the cell voltage change detection type normally found in the 30 minute to 60 minute style of fast chargers. At 60 minutes, the fast chargers can detect full charge safely and not compromise the cycle life of the cells, but that's very hard to do at 30 minutes/charge as the contact resistances of the cells at that high of charge current becomes problematic. That's why most 'smart chargers' at those rates use a pulse method of charge. They dump a lot of current into the cell for a while and then shut off and let the cell voltage come back down to the 'rest' value. This eliminated the contact resistance issue. But, it's still a bit chemestry dependent. So, for the 30 minute chargers, you *really* want to make sure you're just using them on the proper 30 minute cells. IMHO, a 60 minute charger is completely safe and nearly ideal for modern NiMH cells. The 15 minute chargers are only safe for their own specific cells. And, at that, 15 minutes only gets them to 80% of charge. It takes an hour or so after that to get them to 100%. They have to stop before 100% full charge simply due to the danger of overcharging. Think of it, the 2000mAh cells in the Ray-O-Vac 15 minute system charge at over 8A! It doesn't take much overcharge before something horrible happens. I hope that clarifies things a bit. I think we mostly agree, but I just wanted to restate things to make sure we both were properly understood. Cheers, David

I would recommend against this. Modern high capacity NiMH cells form a different crystal structure when fast and slow charged. The fast charge structure yields more capacity and a lower internal impedance--flatter discharge curve. Paradoxically, it's also easier to detect end of charge properly in a fast charger as the rate of voltage change vs unit time is higher in the fast charger. So there is less chance of overcharging the cell and damaging it. Additionally, slow chargers tend to be *dumb* chargers and have no state of charge nor end of charge monitoring. So, they're a great way to cook a cell to death. For me, I liked the Ray-O-Vac 15 minute charge system. I also love their 1 hour charger as a general purpose NiCd/NiMH charger--it'll charge all AA/AAA/9V cells/batteries. I have no experience with Duracell, but that's because I quit buying their products because they didn't perform well. Maybe they've improved.

Pick the NiMH/NiCd setting. They have a discharge curve nearly identical to Li-Fe cells. BTW, how is the battery life? The manual was depressing. That short life time was the main reason I *didn't* buy one. Cheers, David

So, how is the battery life with the Cx? The manual claims 16 hours of 'typical' use while it's 30 and 28 for the GPSMAP60C and GPSMAP60. That's a bit of an issue for some of us. Cheers, David