Batteries, Chargers and Testing for Underwater Photographers
The importance of choosing the right batteries and equipment in underwater photography
By Bill Van Antwerp. Part 1 of a two part series
Let’s face it; today’s underwater photography is completely dependent on batteries of one sort or another. Your camera won’t run without batteries; most DSLRs and some point and shoot cameras use proprietary batteries while some P&S models can use AA batteries. Your strobes require batteries too, some use AA while many use a proprietary battery. Same thing for your focus lights and those of you shooting video have to lug around even bigger batteries for your video lights. This article is the first in a series that will talk about battery types, sizes, charging and testing batteries to make sure you don’t miss a dive because you don’t have any power.
There are many ways to characterize batteries but one simple one is by rechargeable vs. disposable. Most batteries that we tend to use as underwater photographers are rechargeable but many folks still use disposable, single use AA batteries in their devices. One reason for this is that the most common rechargeable battery the nickel metal hydride (NiMH) battery has a voltage that is a bit less than the voltage of a AA zinc/carbon battery. The NiMH battery has an operating voltage near 1.2 V while the standard Duracell or Energizer battery has an operating voltage closer to 1.5 V. The second reason that disposable batteries are commonly used is that they have a very long shelf life.
Typically an alkaline battery loses only 2% of its capacity in a year on the shelf, compared to most rechargeable batteries that can lose 20% of their capacity in a week and 10% per month after that. Unless the voltage or shelf life is critical; we recommend using rechargeable batteries to save money and reduce the environmental impact of disposing of so many batteries. One very recent attempt to increase the shelf life of rechargeable batteries is to reduce the internal discharge rate. The first of these were the Sanyo Eneloop batteries and now there are many other brands of low internal discharge AA batteries.
Choosing a charger
Chargers come also in a variety of flavors. There are chargers that claim to charge batteries in as little as 15 minutes and others that might take 2 hours or more. Faster is not always better since batteries can be ruined if they are overcharged or overheated. In general it is recommended by the battery makers to charge their batteries at a rate that is 50% of the capacity of the battery. For example, a 2500 mAh (milli ampere hour) battery should be charged at a rate of no more than 1250 mA or 1.25A. This means that the type of charger you use can make a difference.
There are several smart chargers that are on the marketplace. Two very nice ones are made by Powerex and by La Crosse. Both of these chargers can set individual battery charging rates, as well as discharge rates and can condition the batteries by controlled charging and discharging.
Maha Powerex MC-9000, a reliable product
La Crosse BC-900, a great performer
Powerex Models MH-C9000 and BC-900
The La Crosse version has almost exactly the same functions but is quite a bit smaller. Both are excellent chargers and will keep your batteries working well for a long time.
Chargers to avoid
Avoid the 15 minute chargers, they have a chance to kill your batteries and invest in one of the smart chargers. For trips, both the Powerex and La Crosse are quite large; we take the smaller MAHA chargers that charge AA batteries in pairs at a fixed 500 mA per battery. These take an hour or more to fully charge 4 AA batteries that are depleted but they appear to be indestructible and work (so far) everywhere in the world at all voltages, frequencies and are immune to interruptions when a liveaboard changes generators.
Taking care of your batteries is important. Salt water is obviously a no-no but there are other dangers. Heating them up to fast is deleterious as is freezing them then warming them rapidly. Most important, dropping batteries on a hard floor like on a boat can drastically alter their life.
NEXT TIME: Bigger is better when it comes to batteries, right? Not Always. Find out why in Part 2: Best batteries for your strobes.
About the author
Bill Van Antwerp shoots underwater as well as topside photos. He is currently shooting a Canon 50D in a modified Subal housing. He uses a variety of strobes with his favorite being the Inon ring flash for macro photography. His website is www.blueviews.net