I use a Princeton Tec EOS headlamp all the time at work. I usually set it on low and it keeps me from falling into holes and tripping over things. I use a flashlight to see and inspect with, but for general navigation, the EOS works out very well.
The EOS is regulated and seems to do a good job of sucking Alkaline cells dry. It is advertised to run about 6 hours on a set of 3 AAA cells on high. On low, I believe the advertised run time is something like 60 hours. Not bad for a set of around 900 mAh cells. Many people have been using NiMh cells and have been pleased with their performance as well. I have not tested NiMh AAA cells at 150 mA, but believe that most brands (regardless of what their label says), should come in with similar capacity.
The EOS weighs 105 grams with the strap and with a full set of Alkaline batteries.
While the EOS is fairly lightweight, I decided to put mine on a diet.
I contacted AW and found out that there are Li-Ion cells that are the same size as AAA cells (10440). Their capacity is a bit low at 320 mAh, but if you parallel them you end up with 3 cells at 4.2 volts and 960 mAh. This is pretty much a direct replacement for the 3 AAA Alkaline cells.
I ordered some cells and put them in. The middle cell has to go backwards and the negative end does not contact the metal strip. A small magnet took care of that problem, and the plastic holder of the light will keep the magnet from slipping around out of place. EDIT: You also have to jumper the contacts at the top and at the bottom. The contacts are in two pieces in both places and you need to connect them together. END EDIT
My EOS went from 105 grams to 98 grams and now is more comfortable to wear, should have the same run time, will have better cold weather performance, I am no longer concerned with self discharge, and because the batteries are rechargeable, I am still enjoying guilt free illumination…
Now I am looking for a place to put a “Lithium Powered” sticker.
I must add that all the standard warnings concerning Li-Ion cells should be adhered to:
These cells are unprotected, so charge them often. If you run them all the way down you will destroy them.
You will need a charger than can handle Li-Ion cells and keep in mind that these are 320 mAh cells. The preferred 0.7C charging rate is 22.4 mA. I am charging at 25 mA. You will need some way to hold the batteries for charging. If you charge them in series, you should make provisions to balance them from time to time. If you charge them in parallel, things on the charging side get easier, but how to hold them becomes more of a challenge.
Don’t charge Li-Ion cells unattended.
Charge on a fire proof surface.
As a foot note…
My wife things I am a bit off because I am running around the house with my head lamp on bouncing my head back and forth trying to see how much of a difference 7 grams makes. I have two EOS headlamps, so I don’t have to change batteries all the time.
I believe there is a noticeable difference, but I also though that my truck had a little more snap to it when I replace the exhaust system and fitted it with Corvette tips…