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Powerex 9v NiMH
By Bill Mills - December 2003

Maha Energy has become the first battery manufacturing company to make a serious effort at marketing their products to paintball players.  Maha’s Powerex rechargeable 9 volt batteries are designed to give players the ability to power their hoppers, paintguns and other accessories without the waste and cost of disposable batteries.

In the last 20 years or so, the rechargeable batteries available to consumers in the US have changed radically.  In the 1970s battery chargers were available to recharge conventional dry cell batteries.  They did a poor job, but could extend battery life a bit.  They weren’t compatible with the newer alkaline batteries, which are today’s prominent, powerfull, single use batteries.  In the late 70s and even on up through much of the 1990s, Nickel Cadmium, or NiCD batteries were the rechargeable batteries most often available in sizes to replace standard Alkalines – AAA, AA, C, D, and 9v. 

NiCDs provide power, but have a number of short-falls.  Their biggest problem is known as “memory effect.”  If a NiCD battery is charged, used, and charged again without being fully discharged, it can develop a “memory” and only accept a charge to the point where it had stopped before.  A battery that should be able to run a device for a half hour might only be able to take enough charge to run it for five minutes.  Another problem with NiCD batteries is that at peak charge they only deliver 1.2 volts per cell, instead of 1.5 like traditional single use batteries.  This difference is small enough that in many applications, it is not a problem.  However when comparing to a 9 volt battery the difference adds up.  A box shaped 9 volt battery is actually a package containing six individual cells wired in series.  A NiCD rechargeable “9v” battery is typically also built with 6 cells, but at 1.5 volts per cell, it only delivers 7.2 volts of electricity when fully charged.  Some manufacturers add a seventh cell to their 9v rechargeables, which delivers 8.4 volts at full charge.  While this is enough to operate many consumer devices these batteries usually will drop below the minimum needed voltage much faster than a true 9v battery, which give them a short service life.

Both of these problems associated with NiCD batteries have put a sour taste in the mouth of many people when it comes to rechargeable batteries.  The problem stems not from the fact that the batteries are rechargeable, but the type of batteries.  Nickel Metal Hydride, or NiMH batteries came into common consumer use in the end of the 1990s.  NiMH batteries are completely immune to the NiCD’s major shortcoming, which was the memory effect.  When first introduced, NiMH batteries tended to be more expensive than NiCD.  In recent years as their popularity has grown prices have come down, and in some cases NiMH consumer batteries can cost as little as 2/3 the price of their NiCD equivalents.

Maha Energy has a history of producing specialized rechargeable batteries and chargers for applications like photography, video production and radio control racing.  Recently they have also begun focusing on paintball.

Maha’s “9v” rechargeable Powerex battery takes a step beyond just using the more modern NiMH chemistry.  Maha has added an eigth cell to the battery’s design, so that when it is fully charged it delivers 9.6 volts of electricity.  Because electronics manufacturers design circuits to allow for a variance of input voltage, it is highly unlikely to ever find a consumer product that will be damaged by the extra .6 volt input, as some alkaline batteries will occasionally deliver that high of a voltage when fresh.

How a rechargeable battery is charged is nearly as important as what it is made of.  NiCD batteries are very tolerant of “rapid charging” at rates of 3 or more times faster than they discharge current.  NiMH batteries on the other hand are best charged at twice their current level, also known as “2c” in battery lingo.  It’s very important that rechargeable batteries only be charged on a charger designed for their specific type.  MAHA Energy produces the MH-C1090F designed to quickly recharge NIMH “9v” style batteries, whether they are of the 7.2, 8.4, or 9.6 volt design.  It is important to note that is designed only for NiMH batteries, not NiCD.

The C1090F does more than just recharge a battery, it recharged up to 10 batteries simultaneously, and then keeps them charged by using what is known as a trickle charge technique.  According to Maha Energy, the charger is designed to charge each battery in 120 to 160 minutes.  In practical use during testing, the charger consistently charged each battery to capacity in less than two hours.  One item of note, is that two of the charging stations on the unit were not as fast as the others.  According to Maha Energy, this was an issue with some of their early models, and has been corrected in the current production runs.  Next to each battery socket is a bi-color light emitting diode, or LED.  While the battery is going through the charge cycle, the LED glows red.  Once the charging circuit determines that the battery is nearly full, because it is drawing less current from the charger, it switches into trickle mode.  In trickle mode the charger delivers a very small amount of electricity to “top off” the battery, and to balance out the slow discharge that occurs over time when a rechargeable battery is not used.  The trickle charge and automatic charging circuit allows the batteries to be left unattended in the charger.  They will be fresh and ready to go when needed.

Another problem associated with some 9v rechargeables is their size.  Their casings are often slightly larger than normal 9v batteries causing a tight fit, or no fit at all in some battery compartments.  Surprisingly the Powerex battery is slightly smaller than normal.  During testing for review it was even easier to fit a pair of them in a Revolution loader than it was to fit Duracell alkaline batteries, or Radio Shack 8.4v NiMH batteries.  The Powerex battery also fit easily into a Matrix paintgun.  The design of the Matrix battery department leaves little to grasp when removing the battery.  With the Powerex battery’s plastic body, there is not metal lip to grasp for removal as with alkalines.  However, with the smaller size of the Powerex, it was easy to use a jewler’s screwdriver to lever it out along its top surface.

In a variety of applications, from Revolution and Ricochet hoppers, to a Matrix LCD and Tippmann A5 E-Trigger, the batteries performed flawslessly, having enough power on a charge to get through a day’s use.  With the Powerex 9.6v battery selling for three to four times the cost of a typical single use alkaline batteries, a frequent paintball player can pay for the cost of the batteries in just a few weekend’s use.  The serious investment for the system is the charger, with an MSRP of just under $70.  It will take longer for an individual to realize the savings, thought some may opt straight for the convenience of never having a need for a last minute battery trip to the store before hitting the field.  For a team however, the charger’s ability to handle 10 batteries at a time makes it a much more practical choice with the cost spread over the entire team.

It’s one thing to see that the batteries do well on the field, but another to quantify how well they do.  To find out how the Powerex batteries stack up against the competition, they were tested in comparison to Radio Shack 8.4v NIMH batteries and a pair of Duracal alkaline 9v batteries.  For testing, the Radio Shack batteries were charged with an RS23-422 charger which is capable of charging either two nine volt batteries, or 8 AA or AAA batteries.

To approximate paintball use, the batteries were used to continuously drive a Revolution loader filled with 100 paintballs and outfitted with a JMJ impeller.  The feedneck to the loader was blocked so that the paintballs would remain in the loader, constantly agitated by the spinning impeller.  Voltage output of the batteries under load was continually measured and as expected, dropped off when the batteries weakened to the point that they could no longer spin the impeller.  It should be noted that the run times measured in the test do not correlate directly to how long the batteries would last in game conditions, as during normal use the agitating motor only spins when there is a ball jam.  The test data was gathered as a means of comparing the lifespan of different batteries in a loader, not of determining how long they would last under field conditions.

As expected, the Alkaline batteries were the top performer of the group by a significant margin.  It seems almost poetic that since they only have one life, it would be a long one.  The Alkaline batteries drove the test loader continuously for 7,904 seconds, or two hours and twelve minutes.

The top rechargeable, as expected with its higher milliamphour rating was the Powerex from Maha Energy.  These batteries ran the test loader for 3,136 seconds, or fifty-two minutes.

The Radio Shack rechargeable operated the test loader for 2,560 seconds, or forty-three minutes.

Interestingly the voltage drop off from each battery type over time (in the graphs above, the red grid lines represent 20 seconds of time) was different.  Both NiMH batteries delivered lower voltage once they could no longer provide the needed amperage to spin the motor, while the alkaline dipped and regained voltage but could no longer deliver the needed amperage. 

It may be tempting to project that the total minutes of motor agitation in the field would be equal to the operation time on the test stand, but in all three tests, once the batteries were given time to rest, they were able to once again spin the agitator against the resistance of the paintballs, indicating that in-field motor operation time will likely be notably higher than the lab test motor operation time, because the batteries would have rest time between agitations.

While the test results showed the operating life of the Powerex battery on a single charge to be 40 percent of that provided by an alkaline battery, Maha rates their battery for 1,000 recharge cycles.  In that context, the battery has an overall operating life of more than 400 times the life of the alkaline, yet its retail price tag is roughly 3 to 4 times as much.  Figuring the cost of the charger and a single battery at roughly 26 times the cost of a single 9 volt alkaline, dollars spent on the rechargeable will go 167 times as far than if spent on an alkaline.  The savings increase when comparing the cost of multiple batteries with the charger.  When comparing rechargeable batteries, the Powerex provided a twenty three percent longer operating life than the Radio Shack 8.4 volt battery, though the two are competitively priced.

Rechargeable batteries are not for every player, sometimes the longer life and ready availability of alkaline batteries can make them better suited for a particular task.  For a regular player, however a little time spent with a spreadsheet or calculator and a look at how often they purchase batteries can quickly determine the savings available through rechargeable batteries like those from Maha Energy. 

 


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