Supplying battery power on a DV shoot can be dangerous business. The ingredients in some batteries make a very toxic soup, like cadmium in NiCad batteries. Proper use and disposal is a personal, professional, and environmental concern for us all. If lithium-ion is involved, improper charging and discharging can lead to catastrophic failure for both power supply and the equipment being powered.
If that doesn't sound risky enough, the improper transportation of some batteries can be a federal offense. Of course, things aren't all bad.
In fact, rechargeable batteries are getting safer, cheaper, and more powerful all the time. For today's handheld DV camcorders, power requirements are about half that of older, shoulder-mount cameras, so batteries are smaller, lighter, and longer-lasting, too.
Nevertheless, when considering your power needs and matching them to products now on the market or soon to be, you should consider several factors, including the following:
• your equipment's technical requirements and operating parameters
• the technical, chemical and electrical specifications of the entire power system (batteries, chargers, accessories)
• the usual price/performance and warranty considerations. You may find that one—or more—power options are required.
The Type Cast
Each of the main rechargeable battery types has its own characteristics, be it Nickel Cadmium (NiCad), Nickel Metal Hydride (NiMH), Lithium Ion (Li-Ion), or hydrogen fuel cell. One of the biggest differences is the power/weight ratio. NiMH has about twice the capacity of NiCad—more power, less weight. Li-Ion batteries produce the same energy as NiMH batteries but weigh even less.
NiMH batteries are more environmentally friendly than NiCads. They do not contain toxic materials like cadmium or mercury.
NiCad (and even NiMH) batteries suffer from "memory effect." If only partially used (or discharged) before recharging, a battery "forgets" it can discharge anymore, and an artificial baseline is created. The battery still works, but may only hold a portion of its original capacity.
In the past, users were often encouraged to run through a battery's full cycle (charge, discharge, charge) every couple of weeks, usually by letting a device run on battery power until no more remains. More and more, however, sophisticated charger systems will do this for you, and eliminate most traces of false memory. It's a matter of some debate, in fact, whether the real cause is chemistry, poor manufacturing techniques, or improper charging techniques. In any case, new technology is addressing this once aggravating issue.
All batteries, however, do self-discharge (depending on battery type and storage conditions, primarily), so a good battery management system that involves some sort of charge/discharge, use/maintenance protocol is recommended.
NiCad batteries are very resilient, and few storage considerations are needed. They work well if fully charged a few days before use (watch for moderate self-discharging and adjust cycle times if needed). It's good if you can fully discharge them at least every five to seven uses.
NiMH batteries should be charged on shooting day (they have a fairly high self-discharge rate). They should be discharged every 30-odd uses, just to be safe. Store them charged, and charge them up every couple of months anyway, even if they have not been used for a while.
Li-Ion (and the older lead acid-type) batteries do not develop memory effect. They have a fairly slow self-discharge rate, so can be topped off a few weeks before use (they handle long-term storage well; keep them at around 40% capacity, and they can sit happily for months). Li-Ions probably charge up the slowest of all, however.
One of the newest battery types is based on hydrogen, a lighter-than-air gas. When hydrogen is properly mixed with oxygen inside portable cartridges, electricity is released—and lots of it. Hydrogen fuel cells offer extended runtimes at reduced weights in comparison with other solutions.
They are not so much recharged as refilled (hydrogen is also available in solid form, as metal hydride, and so cell packs can be swapped easily), and are considered a very "clean and green" power source.
While considering chemistry, life expectancy, and the environment (yes, we are still talking batteries here), we should also devote at least some attention to more obvious, but no less significant features like size and shape.
They've been around for years, and the NP-1 style (a "chocolate bar" to those of us who've been around for years, too) is still the most common form factor for rechargeable batteries. Most manufacturers offer them. The so-called Sony V-Mount is popular, too, and available from other companies. V-mounts can be "stacked" using special brackets for longer-lasting back-up or redundancy power, depending on configuration.
If you're shooting with one of the smaller handheld camcorders (like a Sony PD 150, Canon XL2, or JVC HD10U), you may think a lot of this battery stuff is irrelevant.
Because MiniDV cameras draw half the voltage and a fraction of the wattage of bigger cameras, lithium-ion technology is de rigueur in the DV world. Sony's Info Lithium system has been around for years. The batteries for Canon's XL1 and GL1 are lithium-ion, as are those for most other handheld camcorders on the market. Because some manufacturers use proprietary battery or charger shapes, sizes, and pin configurations, compatibility among brands can be an issue.
It's hard to buy big batteries for smaller DV cameras. Anton/Bauer does have an option, including a Gold Mount plate and a built-in voltage step-down transformer, to accommodate Canon's XL lineup, and other solutions to take large-camera standard 14.4-volt input down to 7.2V output are available, running a second tap for 14.4V output to an optional device, like an on-camera light.
Inside the Chargers
So it's easy to see why most battery manufacturers today call themselves system providers, not just battery sellers. Chargers, for example, now include computer-controlled circuitry for monitoring, measuring, and maintaining batteries. Real-time information about power status and life expectancy in the field, using LCD displays and other readout devices, is also available.
Chargers operate in a sequential or simultaneous mode, depending on configuration, features, and price points. Sequential chargers do one battery at a time, no matter how many slots or connections are available. After one battery is fully cycled, the charger moves on to the next one (there may be some overlap).
Simultaneous units, as expected, charge a number of batteries at the same time (two-, four- and more- slot units are available). The cycle time varies with system specifications, number and type of batteries, overall power capacity, previous discharge state, along with other considerations. Some chargers act as A/C power supplies as well, and may be able to both charge a battery and power a separate device at the same time.
At the end of the day, no matter what battery system you use, you still want enough juice to keep you going until the day really ends. Determining just how long they (and your equipment) will run by referring to industry ratings can be confusing and seemingly contradictory.
There are nominal ratings as well as ranges. Equipment wanting a 14.4V power supply, for example, could be damaged if it isn't able to handle up to 17 volts that may come off a seemingly appropriately rated battery.
An amp-hour(Ah) refers to one amp for one hour, or a portion thereof. If your camera pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) times .333 (20 minutes is one third of an hour), or 6.66 Ah.
The accepted Ah rating time period is hours (a battery is discharged down to 10.5V over a certain hourly period, and actual amp-hours supplied are measured). But ratings at either six or 100-hour rates are given; know which is which or the battery may look better than it really is.
Generally, you can calculate running time by dividing battery watt-hours by equipment power draw. For example, a 90 watt-hour battery used with a 24-watt camera gives about three hours and 45 minutes (90/24 = 3.75; the .75 is a fraction of an hour) of running time.
Avoiding Legal Charges
You should also be aware that international regulations on the transportation of Li-Ion batteries are in place. Check with the National Transportation Safety Board, the Office of Hazardous Materials Safety, or the battery manufacturer to determine what regulations apply and how you should proceed.