March 28th, 2010
Here is a guide to the care and maintenance of SLA or sealed lead acid batteries often used in photographic lighting kit.
This is a particularly dull subject but one that affects a growing number of photographers and videographers who use battery lighting and portable flash on location. SLA batteries are the power house of most portable lighting equipment including Broncolor Mobil kits and Lowel id lights. The batteries have a high capacity, are heavy, relatively inexpensive and if maintained properly will last from 4 to 5 years. However just one extended discharge can destroy an SLA battery and render it useless. Even a near deep discharge can greatly reduce the amount of charge a battery will ever be able to retain.
Some battery chargers are quite good at recovering a battery from a fairly deep discharge by using a pulsing phase cycle that dislodges sulphur build up on the plates but no charger can perform miracles. If your battery has been left to go completely flat then it will need replacing but don’t panic because they are not expensive. In the UK we have MDS battery and Battery Masters among the online traders that stock the most common sizes. In most cases a battery can be replaced without the need for elaborate tools. The battery connectors are usually the Lucar spade type and the leads simply push on to secure. A Broncolor Mobil pack has just four small cross head screws securing the cover to the battery carriage. Undo these and a battery swap can take less than a minute.
An SLA battery does not need to be periodically discharged in order to maintain it’s performance, in fact, it is best kept in a fully charged state. An SLA battery can be kept on charge indefinitely if a high tech charger, like the Ctek, is used. Cheap chargers have no monitoring and can overcharge and destroy a battery if the battery is left on charge for too long. Basic chargers also have poor voltage regulation leading to a shorter battery life.
The Ctek charger is designed to stay switched on and connected to a battery or charging port of a power pack when it is not in use, even for months at a time to maintain a battery in perfect condition ready for instant action. Most high quality flash lighting kits come with a two or three stage switch mode charger. These usually have a high bulk charging rate and switch to a maintenance charging rate when the battery reaches 90% of it’s capacity. Sometimes they show a green light but allow the battery to discharge slowly without maintaining it in peak condition. If you have one of these chargers you should periodically unplug it from the battery, wait ten seconds and plug it back in to restart the charge phase. The charger light will go red or orange to confirm that it is indeed charging the battery.
A Ctek charger has a very low voltage ripple and can stay connected to equipment when it is in use without any risk of damage. The Ctek system was developed to maintain the batteries of supercars like Ferraris and Lamborginis in peak condition whilst they are keep in garages under wraps for months at a time. A considerable amount of research and development went into the technology in a Ctek charger and their slogan is ‘The smartest battery chargers in the world’. I associate the word smart with being able to think rationally and the chargers are certainly not capable of that but they do continually monitor the condition of your battery and pulse life into it as and when required.
Here are links to replacement cells for two of the most popular batteries used in portable photographic flash systems and of course continuous tungsten lighting.
These cells are designed for repeat cyclic use and are perfect for lighting kits that get regular daily use:
12v 7Ah, 12v 12Ah
Lighting systems that spend far more time on the shelf than in use would benefit from cells designed for primarily for standby use:
12v 7Ah, 12v 12Ah
If you are in doubt as to which battery you need consult your equipment manual or speak to one of the team at MDS battery.
The Ah rating on a battery indicates the number of amps it is supposed to be able to deliver continuously for a period of one hour. So a 7Ah battery should be able to deliver 7A for one hour if it is in perfect condition. There is a bit of headroom available on current drain but it would be unwise to draw more than 10A continuously from this size of battery. The equation you need to use to calculate the current draw is Watts = Volts x Amps So if you have a Lowel iD light that is 12v with a 100w bulb, it draws 100/12 Amps or 8.3A This current delivery is just within the upper limit of a 7Ah battery but better suited to a 10Ah or 12Ah battery. Indeed an iD light should in theory run for 50 minutes on a 7Ah battery but in practice 40 minutes is all you can expect from a perfect battery dropping to 20 minutes when a battery is at the end of it’s useful life. The same 100W Lowel iD light will run for just over 80 minutes from a good 12Ah battery.
Warning: The terminals of an SLA battery should never be shorted. A 12Ah 12v battery is capable of delivering 500 Amps in short circuit condition, enough to make screwdriver glow red hot.