Batteries

Oldham lights use Lead acid batteries; these are heavy and bulky. The acid is extremely corrosive if it leaks. In modern lead acid batteries the acid is in gel form. Lead acid batteries must not be left in a discharged state. Although relatively inexpensive they are heavy and bulky so do not make good cave light batteries.

Ni-Cad batteries have been around for many years and are widely understood. They can suffer from memory effect, where they do not take a full charge, however they can be rejuvenated. And although they do not have the energy density of more modern batteries, they are relatively inexpensive and have a long life, and therefore, are ideal for anyone who caves infrequently.

Ni-MH batteries, are considered an upgrade to Ni-Cad batteries, they have higher energy densities, and do not suffer from memory effect. They can be charged, just as easily. However, they only have a life of between 3 and 5 years regardless of usage, and can only be recharged around 500 times.

Li-Ion batteries are a more recent development. They are used in most modern Laptop Computers, MP3 Players and Mobile Phones. They are used in these devices as they have the highest energy densities currently available. However, they have many disadvantages. They are liable to explode if shorted or over-charged; hence, they must always be supplied with an electronic protection circuit. They must be charged carefully in order to prolong their life. They have a short life of 2-3 years even if they are not used. The capacity will start to fall after only 300 charge cycles. Although initially very expensive, as production has increased so their price has dropped.

Battery Life

Batteries have a voltage and current rating. i.e. an FX2 produces 2.4V for 7AH. If we multiple these together we get a power rating i.e. 16.8WH. If we want to use the FX2 battery to power a 3W LED via a switching converter that has an efficiency of 90%, we get a life of: (16.8*0.9)/3 = 5 hours.