The new Garmin eTrex "H" series units use the relatively new MediaTek (MTK) GPS chip instead of the SiRFIII chip in the GPSMap 76/60CS(x) units.
From the comparisons I've read (I don't have either chips), the MTK looks good:
+ Slightly better under under heavy coverage and quicker acquisition than the SiRFIII.
+ Considerably better tracking accuracy than the SiRFIII.
+ Considerably lower power consumption than the SiRFIII.
+ More "stable" stationary signal (doesn't jump around) when you're not moving (though Garmin seems to filter some of this out for its normal display).
- Takes longer to "realize" you're moving (probably due to heavy filtering for that "stable" stationary signal).
- Tends to slightly cut the corner on 90 degree turns (bigger problem on the early bluetooth MTK GPS receivers).
The SiRFIII is still great and was quite a leap forward, but the MTK unit looks even better. A Vista HCx is definitely on top of my short list for receivers to pick up in the near future (Despite the CS(x) rebate).
Also, I don't know what kind of "DC-DC converter" is in that Vector unit, but I would suspect it is a LM317-esque linear regulator. While they have their use, they are at best 40% efficient in converting power (without the use of transistors).
Efficiency is probably even lower when you're trying to convert to a voltage much lower than the input at a low current (I'd estimate maybe as low as 25%).
If you're handy with circuits or know someone who is, there are some very efficient switching regulators (70~90%). Texas Instruments even makes some as efficient as (up to) 96% (needs a pretty heavy load to get that high, though):
http://focus.ti.com/docs/prod/folders/print/ptn78060w.htmlSome capacitors, resistors, a multi-pole rotary switch, connectors, a project box and you'd have a great efficient converter. I have a smaller TI converter in a cigarette lighter power plug like the Vector that I use for a USB-based power port. Works great.
Might be something to look into to get all the power you can out of those solar panels.
I forgot I signed up to this forum long ago.