linehant said:
Doug, I've been wondering how well headlamps would work with the rechargeable batts. What sort of difference is there in the burn time? How about cold weather?
I frequently use NiMH rechargables in my headlamps, winter or summer. Short answer: fine, long answer below.
A quick summary of the characteristics of the 3 most common batt types:
* NiMH:
- 1.25 V
- rectangular discharge curve
- medium low temp performance
- heavy
- good high current capability
- limited shelf life (several months)
* Lithium (nonrechargable):
- 1.5 V
- rectangular discharge curve
- good low temp performance
- light weight
- good high current capability
- long shelf life: 10+ yrs
* Alkaline:
- 1.5 V initial voltage
- tapering discharge curve
- poor low temp performance
- medium weight
- poor high current capability
- long shelf life 5+ yrs
(A rectangular discharge curve means that the battery voltage stayes relatively constant until the cell is exhausted. A tapering curve means that the voltage goes down as the cell is used.)
All of the above battery technologies (except for alkaline in the cold) are fine for most headlamps. The intensity using alkalines will taper off as the cell is used. The intensity using lithiums will stay full until nearly the end and then dimish rapidly (a few minutes). The NiMHs may start a little dimmer (due to the lower voltage), but will hold their intensity until they get near the end.
Many LED headlamps with multiple intensity settings will perform as above. The BD Zenix IQ and Princeton Tec Matrix also include a regulator circuit that keeps constant intensity at a range of voltages (at the cost of drawing more current at the lower voltages) so they will give the same intensity with all of the above voltages.
Burn time? All 3 battery technologies store a similar amount of energy (AA ~2500mAh, AAA ~800mAh) but may dole it out differently. NiMHs and lithiums maintain full intensity for a medium duration. For instance, for my Princeton Tec Aurora with lithium or NiMH AAA batts:
hi ....... 200mA ..... 4 hrs
med .. 100mA ..... 8 hrs
low ...... 40mA ..... 20 hrs
The rediculously long burn times listed on LED lights for alkaline batts also feature a greatly reduced intensity as the batts discharge. The lifetime is determined by your tolerance for a weak light...
Shelf life is important for applications like emergency lights which are likely to sit unused for a long time or low drain applications like smoke detectors. For applications like a weekend hike, one can top off the charge in an NiMH battery just before going.
High current capability is important for applications like digital cameras which have high drain for short periods of time. (Alkaline is a poor choice here at any temp.)
Low temp: NiMHs and lithiums are fine for most winter hiking. I typically carry NiMHs in my headlamp and lithium spares. Covers me in all temps (and keeps the weight down). If I want to minimze the weight, I'll carry only lithiums. Same for my GPS and digital camera.
BTW, Lion (lithium ion, rechargable) batteries, found in many digital cameras, has medium low temp performance and light weight.
Doug
and am looking for a replacement. I am planning on doing some night hiking in the near future, any suggestions for what to replace it with? When I purchased it it was the newest smallest and brighetest one I could find, now there are SOOO many choices.
