Bicycle Lighting - Batteries - Nickel Cadmium
- As a category, NiCads are the Jeckyll & Hyde batteries - the best ones are very good indeed, but more often the cheap units sold in most corner shops are rubbish.
- Also, they are quite difficult to recharge and store properly and so rarely achieve their theoretical potential.
- Their cell voltage is 1.2V (as against 1.5 for primary cells) so when used in pairs the voltage delivered to a 3V bulb is not in theory high enough - however things usually work out OK because the 2.4V is solidly maintained even with a high current drain - whereas the '3V' supplied by a pair of Alkalines very rapidly droops below 2.4.
- Cheap NiCads have a dismal ED - lower even than Zinc Carbon batteries. Some others sold as 'industrial quality' are a little better, but in general the ED varies considerably according to manufacturer and size of cell. They can be very light, and as the charger is cheap value is surprisingly good. These batteries are best suited to commuting situations where value is important and low capacity is not a problem. As with most batteries, simply assess the weight of a cell to get an idea of how good it is likely to be.
- Here is a table of possible 4A-h configurations, to drive a 6V 6W bulb for about 4 hours. Value For Money (VFM) and Power For Money (PFM) figures below assume middle-of-the-road UK prices.
- For the best performance, power-to-weight, see the ED figures.
- For the best value, look at the VFM.
- For performance at a good price, check out the PFM column.
Battery type v A-h wt(g) price charges ED VFM PFM
SLA 6 4.0 850 13.10 100 2.8 90.9 21.4
Cyclon 6xD 6 5.0 1200 25.00 200 2.5 156.7 26.1
NiCad 5xD 6 4.3 675 30.00 200 3.8 98.3 29.1
NiMH 10xAA 6 3.2 350 20.00 100 5.5 38.4 14.6
new NiMH 10xAA 2.5Ah 6 5.0 320 16.00 100 9.0 80.0 70.0
NiMH Dura DR11 6 3.6 360 80.00 120 6.0 20.7 11.5
NiMH 5x4Ah 6 4.0 300 35.00 100 8.0 42 29
Lithium Ion 7.2 3.2 300 120.00 100 7.7 10.5 7.0
Lithium Polymer 5.4 3.2 200 110.00 100 8.6 4.9 4.9