Important notes for NiMH batteries

• Do not completely drain the battery
• Do not overcharge the battery
• New batteries may not reach full potential until they have been 'cycled' 5 times
• Temperature will affect performance

When your lights turn dim and yellow turn them off.

Not all battery packs are created equal, or to be more accurate, not all the cells in a pack are equal. A 6Volt battery pack contains 5 cells of 1.2Volts each (12Volt = 10 cells). While all the cells are tested before and after making the pack they are not exactly the same. This means that at some point one of the cells will run out of charge before the others. When this happens your lights will dim and yellow because you are no longer getting the full voltage. At this time the other cells will effectively be pumping power through the weaker cell in the reverse direction which will damage it.

When charging, do not over charge

Where possible use a smart charger or monitor your batteries to ensure they are not overcharged. NiMH batteries are charged by supplying a voltage higher than the battery rating. Once the battery has been fully charged this power is converted to heat and causes degradation of the battery.

Smart chargers can work in two ways and some use both. The first is to monitor the voltage of the battery and the other is to monitor the temperature of the battery. If you are not sure that your charger does one or both of these checks then it pays to monitor the battery yourself and remove from charge if it gets noticeable hotter or you believe that it has had sufficient time to charge.

A smart charger will pay for itself the first time you save a battery.

New batteries should be 'cycled' 5 times

Most manufacturers advise users that batteries will not reach full potential until they have been charged and discharged (cycled) 5 times. Some suggest doing this before using the lighting system on your bike.

The rationale behind this is that each cell needs to be fully cycled at least once before it can deliver maximum power. To allow this to happen to 5 cells of varying output may require 5 charges. So for a 12 volt battery you may need to cycle the battery 10 times.

Unless you absolutely must have full power on first use why not use the light on a ride, bearing in mind that it's run time may be slightly shorter. To do this properly, when you complete your ride leave the light on until it dims and then charge the battery.

Two things to be aware of when stationary discharging a battery using riding lights. First the lights will heat up and not be cooled by moving air so make sure it is in a cool place or you have a fan to run over it. Second you are reducing the life of your bulb, and even more so if it overheats.

All this initial attention will provide you with a good idea of the runtime of your battery with your own lights. BTW why waste battery and bulb time on nothing, get out and ride even it's it's just around the neighbourhood for a while.

Temperature will affect battery performance

NiMH batteries work well across a wide temperature range, but their performance will be affected by extremes. For most of us the extreme to consider is cold. At below freezing a NiMH battery will perform like a lower powered battery. If you think about the metal housed nightstick batteries hanging off your downtube in the middle of the night as you ride along at 15km/hr or more, it is easy to imagine that the temperature of the battery inside may drop to less than the ambient.

If you are riding in cold conditions consider that you will effectively have less power and shorter battery life, or think of ways to keep your battery warmer. With the smaller flat packs I like to keep them in a neoprene sleeve that not only protects them from bumps but also insulates.

Warmer temperatures will cause the battery to self discharge while in storage. So leaving a charged battery in a hot car before a ride may leave you with less battery life than you anticipated.

Links

BikeCurrent FAQ http://user.fundy.net/cyclist/bikecurrent-FAQ.html or http://www.purl.org/bicycling/FAQ/bikecurrent-FAQ/

www.myra-simon.com/bike/lights.html http://www.myra-simon.com/bike/lights.html

Duracell NiMH Technical Bulletin (PDF)http://www.duracell.com/OEM/Pdf/others/TECHBULL.pdf

Disclaimer: I have no connection to any of the brands, manufacturers or retailers mentioned above.
This article is provided solely for the information of the reader and it is their responsibility to determine how it may be used. Hopefully this means they get something out of it and enjoy good and safe night riding.