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MH-C401FS and Powerex AA Batteries
By Bill Mills - June 2005

Nine-volt batteries aren’t the only style used in paintball.  AA size batteries see use in HALO loaders and both AA and AAA sizes are commonly used in FRS radios for both field staff and scenario players.  As with 9-volts, players have options of buying and tossing single use alkaline batteries, or going the rechargeable route.  The upfront cost of a charger and rechargeable batteries is usually significantly more than a set of single use batteries, but over time considering the number of times the rechargeables can be used it is typically less expensive than a comparable number of single use batteries.

Those who have read the WARPIG.com review of the Powerex 9.6-volt NiMH batteries will already know what’s up with rechargeables and why NiHM batteries have gained so much popularity over the older NiCD technology.  In addition to their Powerex 9.6v models, Maha Energy also produces AAA, AA, C and D cell rechargeable Nickel Metal Hydride batteries.  Of course, to go with them, they also produce chargers.

The Powerex MC401FS battery charger is designed to work with Powerex or any other brand of NiMH AA or AAA rechargeable batteries.  The charger can be powered by either of its two included power cables.  One is an AC wall transformer, for home use, and the other is an automobile cigarette lighter adaptor, giving the charger versatility of use at home or in the field.

The charger has four charging bays, each with its own circuit.  This allows batteries to be added and begin charging at any time, regardless of what is happening in the other bays.  In contrast, some other AA chargers require that batteries can only be charged in pairs, or sets of four.  

The problem with paired chargers is that they cannot properly charge an odd number of batteries.  Using a battery in a single battery pocket flashlight, or using three in a radio means having two sets of batteries so they can both be drained, and then charged in even numbers.  The alternative, of putting a charged battery in with the discharged batteries on the same charging circuit would lead to possible overcharge damage of the one, and or undercharging of the others.  

These potential problems are avoided with the 401’s individual charging circuits.  Each circuit is linked to a bi-color indicator LED.  It lights red while a battery is charging, and green once it has been charged and is being given a top-off trickle charge.  If the charging circuit detects an error preventing the battery from charging properly, the LED will flash red. 

Each battery bay can charge either a AA battery or a AAA battery, but it can not hold both simultaneously.  Another advantage of the single battery charging circuits is that AA and AAA batteries can be mixed in the charger.  An AAA can charge in one bay while AA s charge in others.

Another feature of the charger is the option to select fast, or slow charge times.  This is a single slide switch setting that affects all four charging circuits.  In fast mode, the charger takes about an hour and a half to charge one to four AA batteries (about 2/3 that time for AAAs.)  In slow mode, the same batteries take as much as 5 hours to charge.  While Maha Energy promotes this mode as something that will extend the life of the batteries, through cooler temperatures, the slow charge also appears to put a more thorough charge in the batteries.

The 401 is equipped with a clear door cover, which closes over the battery bays.  While it is an extremely rare occurrence (the author has never seen it happen in 25 some years of using rechargeable batteries) it is possible for a rechargeable battery to overheat and leak or spray its caustic electrolytes.  The closing cover is a nice safety feature to protect against a very unlikely problem.

An important difference to note when comparing Alkaline single use batteries to their rechargeable counterparts is voltage.  A single cell (AAA, AA, C or D) alkaline battery will output 1.5 volts.  A single cell NiCD or NiMH battery on the other hand will only output 1.2 volts.  While this difference in voltages seems small at only a tenth of a volt, it adds up when the batteries are used in series.  In a HALO loader, for example, 6 AA alkaline batteries in series provide 9 volts.  In the same configuration, 6 NiMH batteries will only deliver 8.4 volts.  While this may seem to be a problem, most battery-operated products can handle the lower voltage without trouble.  This is because as batteries are used, the voltage they deliver decreases.  At some point it will be too little for the device to operate.

A nice extra feature included with the Powerex 200 Mah AA batteries is a clear plastic case.  The batteries are sold in sets of four, and the convenient cases hold 4 AA or AAA batteries.  While they may not seem important, they proved handy during review, especially when keeping a spare set of batteries in a gear bag.

In use, the MC401FS showed a significant difference in performance offered between the Fast and slow charge modes.  While both modes feature an alternating voltage charge, designed to have the same anti-memory effect as discharging a battery prior to charging, the slow charge took significantly longer, especially with four batteries as compared to two, and resulted in a more effective charge on the battery.  

After having gone through a few charging and use cycles, the AA batteries were coming off of the charger with a charge of 1.3 volts when fast charged, and an impressive 1.4 volts when slow charged - 0.2 volts above what is typical for their battery type, and only 0.1v less than their single use alkaline counterparts.  Put to use in radios and a camera flash, the batteries worked well with no problems.  Slow charging produced very noticeable results in terms of how long the individual products could be used on a single charge.

Sow how did they stack up in terms of long life?  To get a look at how they discharged over time, 6 batteries were run in series with a load, and their voltage measured over time, as the batteries drained.  The load used for testing was a speed 280 motor with an 8 inch propeller to keep the motor cool and provide load (the energy a motor draws depends largely on the amount of work it is doing.)  The motor was wired in series with a variable resistor that was used to limit current in order to prevent overheating of the motor at the start of the test.  Once set, the variable resistor was locked to provide the same resistance for all of the tests.  As the motor spun the fan, it drew energy from the batteries.  As that energy was used the voltage they were able to supply to the circuit decreased until eventually they could no longer spin the fan.

[Editor’s note: In order to more closely duplicate actual paintball use, a significant amount of work was put into developing a test stand involving multiple loaders that would feed paint continuously, putting load on the batteries by re-cycling paint back into the loader after it had been fed.  This unfortunately proved to be impractical, as a system that could reliably feed paint or reusable practice balls for more than one hour without stopping or jamming was not achieved.  Two loader products literally burned out during the test stand development process.  Thus, a more generic load to show battery drain over time was used instead.]

To have a frame of reference, the slow charged Powerex AA batteries were compared to Duracell Copper Top single use alkaline batteries and Radio Shack NiMH batteries charged in a Radio Shack 23-422 charger.  In comparing the rechargeable batteries, how they were charged was as likely as important a factor as the batteries themselves.

When reviewing the battery drain graphs produced, it was clear that the Powerex batteries had outperformed their Radio Shack counterparts on the test aparatus.  What was surprising was how well they compared to the Duracell single use Alkalines.  While they did not reach the same peak voltage, and did not deliver as high a voltage over the useful life of their charge (the time at which the motor was spinning at a good pace) their useful life was very close to that of the single use batteries.  Additionally, rather than dropping off the voltage they delivered as abruptly, the Powerex batteries continued on some time more, delivering less voltage than during the initial phase of their discharge.  

The Powerex AA batteries and MC401FS proved to be a flexible and potent combination, with the ability to charge at home or in a car, slow or fast, and a useable charge life when slow charged that is near enough to alkaline batteries to be compared.
 

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