Camcorder Battery Charger Choices: Matching Power to Purpose (page 3)

SIDEBAR 1: The Memory Dilemma

Probably nothing in the world of video power is more misunderstood than the term "memory." This word has been a catch-all for countless numbers of bad experiences videographers have with their powering products.

But memory is a coined term applied to a phenomenon more correctly referred to as voltage depression. Voltage depression is a small dip in voltage that starts near the end of discharge, and then over many charging cycles, slowly moves towards the beginning of the cells discharge. This voltage drop may fool the user into suspecting a loss of battery capacity because the equipment being powered usually reads the drop for an empty power pack, resulting in a premature shutdown.

Ni-Cad cells experience voltage depression after a period of overcharging. . This occurs when either a charger fails to sense charge completion or the user does not follow the battery manufacturers instructions. The problem becomes extremely evident when a fast 2-hour charger is paired with a battery that is not designed to charge in less than 12 hours. The excessively quick charge, combined with inaccurate power sensing, causes voltage depression in many batteries.

Luckily, the problem is easily erased. But this is little known amongst many users. The slight dip in the discharge "profile" ( a graphical representation of the battery's power discharge over a period of time) that results from the cells voltage depression can be erased. A proper discharge profile is restored by discharging the pack fully and recharging it.

SIDEBAR 2: The Cell Choice

There are really only two classes of batteries used for auxiliary video power; Lead Acid and Ni-Cad. Lead acid cells, which have been around since the mid-1800's, have the advantage of being very affordable to the videomaker. Able to withstand poor charge habits and high rate discharging, lead acid batteries have no memory effect. And, the cells can be stored for long periods if they are exposed to a constant or pulsed "float" charge. One major disadvantage of the lead cell is its low energy-to-weight ratio. This means that lead acid type batteries weigh substantially more than a Ni-Cad power source providing the same power. Short cycle life is another downfall.

The power-to-weight ratio of Ni-Cad cells are excellent, weighing 20-50% less than other types of equivalent power. These batteries however are traditionally higher-priced than their lead-acid counterparts. Memory is bantered around as a problem of Ni-Cad energy sources, but their discharge profiles are superior, as is their ability to deliver stable voltage to any connected video equipment.

The bottom line; lead acid cells are great for low-level consumer work where initial cost of the power source is a factor. For the serious and responsible videographer who looks at equipment as an investment in his future Ni-Cad batteries are a must.

--MSB