[bike] lighting essentials - recharging those batteries

[David Morse]

Winter's coming, and that means night riding. Bike head lights and
tail lights have made huge strides in the last few years, but nobody
ever talks about powering them. This post is about recharging those
lights using high quality rechargeable batteries you can buy at any
Walgreens or Kroger, with special attention to the chargers for
commuting.

But first back up and review the four methods of power, and briefly
why I currently tend towards NiMH rechargable batteries versus the
other technologies.

1) Bike dynamos: These power the lights from the forward motion of the
bicycle. They have various pros and cons, which I should not really
get into here, except to say that they are the most sustainable
solution if you can deal with the significant retrofit and monetary
hurdles to installing them. In a perfect world, all transportation
bicycles would have them built in.

2) Proprietary battery packs: These are typically used to power very
high-power headlights - 300+ lumens. They are usually Lithium Ion
(Li-ion) or some such advanced/expensive cell. They are light weight,
and typically come with their own rechargers. For this reason, they
are favored by people in bicycle sports, and to some extent by
commuters. You can't beat their photons-per-pound performance!
However, they have a downside - if the battery wears out (and anyone
with a cell phone or laptop knows this happens), then the owner is at
the mercy of ONE COMPANY to support their product. This can become
impossible if the company has gone belly up or no longer makes that
model - many working multo-hundred-dollar lights go to the junk heap
for this problem every year.

3) Disposable batteries in lights. This has become a trend with watch
batteries in tiny lights, which are fine for occasional riders who
might get stranded in the dark, and as back ups, but they're not
really serious for people planning to spend 5+ hours a week pedalling
in darkness. AAA and AAs in headlights gets pricey real quick, and
trying to squeeze the last bit of value out of a tail light that's 90%
gone strikes me as penny wise and pound foolish. Avoid 'em.

4) Rechargable batteries in lights designed for Alkalines. Nickel
Metal Hidride (NiMH) has improved every year, and is now a very good
technology. NiMHs are very affordable: $2.50 per cell at Walgreens,
and each cell is good for hundreds of uses - about 1 cent per charge!
Wow. That's what the rest of this post is about.


NiMHs have a higher energy density - especially in high-drain
headlights. For example, my light manufacturer estimates 20 minutes
out of Alkalines in my high-power headlight, or 2 hours with NiMHs.

One bummer: NiMH AA and AAAs produce a hair less voltage than
check-out-counter alkalines, and work in the same lights, though
slightly dimmer. However, since LED lights are doubling in brightness
about every 2 years, this lessened intensity is just a drop in the
bucket, not worth worrying about.

Using NiMHs also has a subtle advantage over the Li-Ion battery packs:
you have vendor independence and modularity. First, if your battery
wears out, you can replace it easily (I retire worn-out headlight
batteries out to lower drain devices, like flashlights). Secondly, if
you're going for a Really Long Ride, you don't have to mail away for a
second battery pack, you just go get the retired batteries out of the
flashlights. Thirdly, the charger is also independent, and can be
replaced. Heck, if life finds you low on juice, its often possible to
borrow a charger at a friend's place.

The charger deserves special attention. Its the only way to judge to
the health of your batteries. A really good charger can tell you a lot
more than just "this battery is charged now". It can tell you how big
a chunk of energy each battery can hold. Its good to group batteries
from the same blister pack together, because they wear better, but
sometimes one gets out of sync, and you can nurse it back to health
with a good charger.

So what're the pitfalls in battery chargers?

$10 chargers that you buy in Walgreens will be trickle chargers. These
have their place, but its not commuting. They can take up to a day to
charge AAs. You need something that works while you're sleeping - less
than 8 hours is a requirement. They are gentle on the batts though,
and you can't really hurt a battery with these guys, which is nice.
They're cheap, I'd get one.

$25 chargers tend to be fast chargers. They put a dangerous amount of
juice into the batteries, relying either on a voltage spike or the
cell temperature to figure out when to stop. Sometimes they miss this
cut off, and electrocute the battery, which will hurt it I'm told.
Bummer. They don't have any feedback other than one light per cell,
that says either "charging" or "charged".  Feh.

The above chargers are what most people these days have. However, most
people don't depend on their batteries day in and day out to keep them
from becoming roadkill. We do. For that reason, investment in high end
chargers is warranted. These chargers can tell you more about your
batteries than a single light. These two models lead the pack:

  MAHA MH-C9000 Wizard One: $60. (tested by me for last ~3 years - works!)

  La Crosse BC-9009: $40 (plus includes $20 of free batteries.)

There's a great compartive review of the two of them here:
http://www.amazon.com/review/R26DDCWZ2JG3HP/ref=cm_cr_pr_viewpnt#R26DDCWZ2JG3HP

The bottom line is you'll want the LaCrosse and maybe a $10 trickle
charger for back up. Its as cheap as vastly inferior fast chargers you
can buy at Walgreens.

You'll want to read the instruction manual: if you treat it like a
toaster, it'll toast your batteries. You need to treat it like a
microwave oven, and build some common-sense when it comes to charging.
If you can't deal with this, just buy a cruddy $25 fast charger, and
prepare to fry. In exchange for reading the manual, you'll be able to
see how much juice each battery has absorbed, and charge batteries
both quickly, reliably, and fairly gently.

There are really three aspects to a well-lit bike: the headlight set,
the taillight set, and the charger. Don't skimp on the charger just
because its not attached to your frame. Without power, lights are just
dead weight. With power they keep you visible. Hooray for NiMH
rechargers!