Lead Acid vs NiCd batteries (c) 1997 Marty Goodman
Folks often ask me about which battery to get with their bicycle lighting systems: Lead Acid or NiCd batteries. This is intended as a "canned" first response to such questions.
The two most common technologies of rechargeable battery used in bicycle headlight systems are Sealed Lead Acid ("SLA") and Nickel-Cadmium ("NiCd"). Low to medium price ($70 to $150) systems will feature SLA batteries, and medium to high priced systems ($140 to $400) will feature the NiCd batteries.
The short version of my advice:
If you do a great deal of night riding, such as many nightly commutes per week, you should get a NiCd battery-based system. If you do only occasional night rides, you'll likely do fine with a SLA-based system. But in either case, you will probably be VERY wise to invest in a third-party battery charger, and NOT use the battery charger supplied with the system you buy.
(a) battery characteristics
Lead Acid batteries are about 2 to 4 times less expensive at time of purchase than are NiCd batteries.
However, NiCds, IF PROPERLY CARED FOR (this is a key operative qualification!) can be recharged 3 to 5 times as many times before they wear out as can be SLA batteries.
Cost of a high quality third party charger for either system is roughly the same ($45 to $90). Note that SLA batteries require a DIFFERENT charger from that required by NiCd batteries.
Overall, NiCd batteries are at least as inexpensive, and probably actually somewhat LESS expensive a source of power than SLA batteries IF you are using them frequently, over the course of their total life. However, if you are using the battery infrequently, for, say, 20 rides per year, then the more expensive NiCd will probably die due to its shelf life expiring before you use all its available charges.
NiCd batteries are, overall, about 30% lighter for a given amount of power capacity than SLA batteries. A significant, but not utterly overwhelming difference.
SLA batteries retain nearly their full charge for two months or more just sitting on the shelf, unattached to a charger. NiCd batteries lose about 1% of their charge per day when sitting on the shelf, due to internal "self-discharge".
NiCd batteries have a flatter voltage vs time curve during discharge than do SLA batteries. This means your lights will remain relatively more constantly bright during the entire useful discharge life of the battery with a given lighting system than would be the case for a SLA battery of comparable amp hour capacity and voltage.
BOTH NiCd AND SLA batteries can be severely damaged by being deeply discharged to down below 75% of their rated voltage. With either system one must never run the battery "into the ground", letting ones lights go from yellow to orange to dim orange. TURN YOUR LIGHTS OFF when they get noticeably yellow, else you risk permanantly damaging your battery.
Many ignorant folks claim NiCd batteries are subject to "charge memory". This is false. As used by cyclists for night lighting applications, there is NO "charge memory" problem with NiCd batteries. PERIOD. I can give you a detailed explanation of the myth of "charge memory", and why so many folks make such utterly ignorant and false statements about it, if you wish to get in touch with me about this.
Some manufacturers who supply SLA batteries with their lighting systems (such as VistaLite with its VL4xx systems) choose the Hawker Industries (formerly called "Gates") Cyclon type SLA batteries. This particular make and model of SLA battery is significantly superior to ALL other SLA batteries. If you are replacing a SLA battery in your existing lighting system, get a Hawker Industries Cyclon battery pack (available in 2.5 amp hour and 5.0 amp hour six volt modules). These offer greater useable battery capacity for a given amp hour rating, are able to withstand deep discharge somewhat better than ordinary SLA batteries, and they last thru more recharge cycles than ordinary SLA batteries. Interestingly, the retail price for a Hawker Cyclon SLA battery is not all that different from the price of a similar ordinary SLA battery. Power Sonic (headquarters in Redwood City, CA) sells Hawker Cyclon batteries. Locally in Berkeley, Al Lashers can order and sell these batteries.
(b) charger issues
With the exception of the Nite Rider Digital Pro 6 and Xcell Pro (formerly called NiteHawk) lighting systems, virtually bicycle lighting systems on the market supply inexcuseably cheap, often quite destructive to the battery type of chargers. The problem is that with most supplied chargers, they charge the battery rather slowly (require 10 or more hours to provide a full charge) THEN then keep JAMMING current into the battery after it's full, heating it up and ultimately destroying it. MANY cyclists have destroyed their $140 replacement cost NiCd water bottle battery by leaving it hooked up to the charger for some days or weeks.
While NOT a "smart" charging system, the NiteRider Xcell Pro and Digital Pro 6 systems do have a reasonably safe "set it and forget" charging system, tho only when used with their supplied battery. Their system charges the battery at a modest rate for 10 hours, then a timer switches over to a 3 times slower charging rate for maintanance of the battery. Their system is not a "smart charger" in that it DOES NOT in ANY WAY sense actual battery condition.
It's relatively easy to make a cheap but safe "set it and forget it" charger for SLA batteries. All that's needed is a voltage regulator, which adds about $1.00 to $2.00 at time of production, or at most $10.00 at time or retail sale, to the cost existing bicycling lighting systems. Amazingly, few if any commericial systems provide this, and instead provide an UNREGULATED DC power supply, which has the potential (liklihood, actually) of destroying the SLA battery if left attached. NiteRider MAY provide such a safe SLA charger in their new product, the "Trail Rat". I've not yet had a chance to analyze this new product on my lab bench.
To more quickly charge SLA or NiCd batteries (full charge in 2 to 4 hours), one needs a "smart charger". Such a charger senses battery condition during charging, pours current into the battery as long as the battery needs it, senses when the battery is full, and then cuts back to a much reduced current flow (or pulses of current at intervals) to keep the battery filled without harming it.
This kind of a very smart charger is a nice convenience with a SLA battery, but not necessary in that a simple voltage-regulated "trickle" charger will usually do the job fine for cyclists. Smart SLA chargers can be purchased from Power Sonic, at a cost of about $50 to $80 for chargers appropriate to existing bicycle lighting systems. You have to add your own cable, of course, to attach the charger to your particular system. Tinkerers should note that a proper trickle charger for SLA batteries is a regulated power supply set to 6.90 to 6.95 volts for a "6 volt" SLA battery, and to 13.8 to 13.9 volts for a "12 volt" SLA battery.
NiCd batteries really benefit from a proper smart charger. Unfortuately, one has to press into service chargers made for other purposes if one wants a smart charger for one's bicycle lighting system. Or make one oneself from scratch. I've done both, successfully. Certain DeWalt and Black and Decker power tool chargers can be converted into very effective smart chargers for bicycle lighting system batteries. The DW9106 and DW9104 in particular are good choices. Some cam-corder and cell phone 6 volt NiCd battery chargers may be suitable as smart chargers for 6 volt NiCd bicycling batteries. I've built from scratch two smart chargers for my battery systems using a Maxim MAX 713 smart charger controller chip. Both work very well. Some have used the more modern 2002 NiCd smart charger controller chip made by Maxim, Benchmarq, and Unitrode. Contact me for details if interested.
---marty
MARTYGOODMAN@delphi.com
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