Welcome to the Wonderful World of Batteries
Tips by William Bridges
Synergistic Batteries Inc.

www.synbat.com

Battery Basics

NEW -- Marketing Batteries --NEW

The Wonderful World of Batteries
Marketing

In this day and age it is increasingly difficult to buy a product that is not skewed in some way, shape or form, by the marketing department. "you too can have the best product since sliced bread". Personally I think the toaster is better then sliced bread.

There are batteries being sold that say things like "matched by voltage", "low resistance battery bars" and "zapped cells". Some of the marketing ploys are actions performed on cells, some are things attached to cells and some are completely unfounded.

Zapped cells: Definition - A half Farad capacitor is charged to 90 volts then shorted to the positive and negative of a single NiCd cell. The idea is to get a higher voltage per cell and a lower internal resistance for a few charge discharge cycles. The reality is that it permanently shorts several wraps of insulating material. The battery has a decreased capacity, a shorter overall life, and has a higher price to the end user. When it is done on NiMH cells it loses even more capacity, and length of service then NiCd's.

Matched by Voltage: Cells are grouped together by voltage. It's a good idea if it had any merit to it. when you charge a battery it is charged to a higher voltage then it will read after it has rested. when you discharge a battery the voltage will rise again after it has rested. So are they matched after they have been charged? if so how long have they rested? have they been matched after a discharge? if so how long have they rested? Are they matched just after they come in the door from the factory? has the factory properly formed the cells? Has the factory run one cycle on them or several?
There are a lot of questions which can not be answered here. Not to worry though here is the answer your looking for; even if you know all of the information of a batteries conception from raw material until your door.
After exact charge and discharge cycles, and after timed rest periods.
There is no way to match batteries by voltage because every cell is unique.
each battery has it's own personality, a set of traits that only it has.
even if the voltages match, the internal resistance does not. If the internal resistance matches then the voltage does not.
The only way to match cells is a capacity test. Then your problem becomes discharge rate, cells matched at one discharge rate may not be matched at a higher or lower discharge rate.

Matched by internal resistance: See "Matched by voltage" The biggest difference between matching batteries by voltage and internal resistance is now we can paste a number on a cell that looks good but is different every time you test it, and it's not linear. Depending on age, voltage, discharge rate, number of cycles, humidity, temperature, test procedure, test equipment and math skills, internal resistance can change. Drastically in some cases. The way most people determine internal resistance is: Battery voltage with no load . Minus . Battery voltage under load . Divided by load.
This seems to be the simplest method with the least amount of equipment, In no way is it the most accurate. It should only be used as a guide.

Matched by capacity: The only way to match cells. The point of matching cells is not to confuse people, not to give you the lowest IR, the point is to have a battery pack that discharges evenly across every cell so your voltage stays higher under any load. If the cells reach their discharge cutoff at different points you have a battery that prematurely fails while under load.

Low resistance battery bars: This seems to be a debate between copper battery bars versus nickel tab stock. Copper has a lower resistivity then nickel. However, dc energy travels on the skin of a conductor, ac energy travels through the core of a conductor. When you wire your house with ac you use solid core conductors, when you jump start a car you use some 4 gauge cables with thousands of strands. If you weld two pieces of tab stock onto the cells, you have just doubled the surface area and decreased the resistivity below copper. Something else to mention is that this usually does not even come into play considering the resistance of the batteries is greater then either the copper or nickel.
There is another reason to have batteries welded with nickel tabs over soldered with copper bars. Heat. If you can hold a penny between two fingers and get a good solder joint with a copper bar, you have not damaged the nylon separator between the positive button and the negative can of the battery. The nylon separator has a melting point of about 200 degree's.
typical soldering is at 600 to 750 degree's. Now I completely understand on another point why the RC industry chose battery bars, they don't have to pay for a spot welder. $19.95 at radio shack for a soldering iron, over $7,000 for a good spot welder, and anyone can make battery packs at home, the problem is that they don't last.

General marketing: My battery pack is better than your battery pack because you have white shrink wrap on it and mine has flames. The look of a battery has nothing to do with how well the cells are made and how well it is assembled. If a battery pack is stuck together with gum and covered with duct tape but out performs the one with the pretty flames, then you know who spent their money on marketing and who spent their money on building a good product.

I realize that not all of the "marketing schemes" are covered here, there is a new one every day. So if you have something specific to add, or If you have any questions the forum is open for discussion.

William Bridges