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WThesing 07-30-2006 12:40 PM

Battery Clinic (Chapters I and II & Follow-up Q&A)
Battery Clinic - Chapter 1

For those of you that use your metal detectors enough to invest in rechargeable batteries, I hope that this little article is helpful. I will try to shed some light on the differences, as well as some of the technology in order for you to make informed decisions. This should save you some frustration as well as money in the long term.

First off, some basics: We are mainly concerned with two types of battery technology. Chemical cells are those which give off a current through chemical reaction, such as lead / acid cells, and the more popular alkaline cells. These are two different chemical technologies, the alkaline being the newest and generally having the longest duration or life expectancy. Both of these types are single use cells with an output of 1.5 Volts per cell. When the chemical reaction slows down due to depletion, the current output also slows, and eventually ceases.

The other type of technology would be the multi-use, or rechargeable cell. They are available in nickel cadmium (Nicad), nickel / metal hydride (Nimh), gel cell, and the newest technology, lithium polymer (Lipo). For our usage we will be concerned with Nicad?s and Nimh. Of the two, THERE IS A DIFFERENCE !!!! Nicad?s are designed to be used in a full charge to full discharge cycle. This means that from full charge they are to be used to what is considered optimum discharge, which is 50 % voltage drop or lower. Both Nicad's and Nimh's have an voltage output of 1.2 Volts per cell, so we are looking at .6V or lower. Incidentally, the difference in voltage output between single use and rechargeable cells will not matter in today?s electronics.

Nimh's are a newer technology than Nicad. The advantage is that they can be recharged at any point in their use cycle without any ill effect. When Nicad's are charged without being fully discharged, they develop what is termed as a "memory". This is a condition which prevents them from reaching a fully charged state. It will eventually shorten the cell life considerably. If either of these types of cells are cared for and maintained properly, they are capable of hundreds of recharge cycles, thus saving the purchase of another set of single use cells.


The single use cells may provide a slightly longer operational time ON AVERAGE, but not by much. They also have a more gradual voltage drop-off than rechargeables, but this really doesn?t affect performance of the detectors, since their circuitry is designed to operate in millivolts. One of the main terms you should be concerned with is the CAPACITY of the cell, which is its rating in AMP HOURS. For our purposes the cells are rated in Milliamps or Milliamp Hours (Mah). This is similar as to how big a gas tank you have, or the amount of electrical "fuel" stored in the container or cell. That amount of current storage or "CAPACITY" is referred to in battery terms as the value "C". Example: a 2000 Mah capacity cell would have a value where 1C is equal to 2000 Mah, 1/10C = 200 Mah.

Not all rechargeable cells are created equal!!!! When purchasing, be concerned with the cell capacity. The higher the milliamp rating, the longer you will be able to use the cell before needing a charge. Generally speaking, the higher the rating, the more costly the cell. This of course depends on where you buy them. There are also differences in quality of cells. Generally those manufactured by Sanyo and Panasonic are the best. They are marketed under numerous different labels such as Eveready, Ray O Vac, etc.

As of this time, the best AA cells that I have found that are readily available, have a good capacity, and are reasonably priced would be the Eveready 2500 Mah Nimh. They also make a AAA 850 Mah Nimh cell. I have purchased the AA's at about $1.10 per cell in packages of 8.

I will be adding to this article when time permits. Chapter 2 will deal with recharging. :grin:

WThesing 07-30-2006 03:15 PM

Battery Clinic Chapter Two
Battery Clinic - Chapter 2


We are obviously discussing rechargeable cells here. No attempt should be made to recharge ANY type cell designed to be disposable single use. Such attempt may cause fire, explosion and severe or fatal injury.

In order to understand some of the dynamics that come into play, I must first make mention of some of the terminology and principles, as well as their abbreviations.

VOLTAGE (V) = Electrical pressure. Think of circuitry (wires, etc) as pipe. Only a given amount of water can flow through a pipe at a maximum pressure. The same applies to the amount of current that can flow through a circuit. Thus we have circuits designed for given loads such as 6V, 12V, 24V, 120 V, etc.

DIRECT CURRENT = Current direct from source without fluctuation. Source would be from battery or generator. Positive and negative poles remain the same. This is what we would be dealing with for our battery use.

ALTERNATING CURRENT = Current that shifts the polarity a given amount in a given time frame. A good example is our house current at 120 V at 60 cycles per second ( 60 Hz). The Hz (Hertz), is the FREQUENCY of alternation. We use this in our homes to minimize voltage drop over distances in transmission lines.

AMPERES (A) = The amount of current. For our cells and circuitry we are talking MILLIAMPS (Ma).

OHMS = The resistance that is within a circuit, or the negative effect slowing down the travel of electrical current. Kind of like driving a car uphill verses traveling level, more power is needed going up hill.

CAPACITY (C) = The capacity of a fully charged cell in MILLIAMP HOURS (Mah)

Since most of our detectors use AA cells, I will gear this accordingly. I also own a detector that uses 9V cells, and I have some small electronics that use AAA cells. The principles will still remain the same.

1. Use a charger designed for the size cells you are using. A charger that OUTPUTS too many AMPS or too HIGH a VOLTAGE will only fry your cells. More on this later.

2. Most inexpensive chargers are designed with no frills. Put your batteries in them, plug into the wall, and forget about them for a day or two. NOT SO FAST !!!!!!!! The majority of these type chargers (Wall Warts) have no internal switching circuitry to determine when the cells are fully charged. They will continue to output current into the cells after they have reached maximum capacity. The result will be a build up of heat that will ruin the cells after a given length of time. The simple solution is as follows. Plug the "Wall Wart" into a timer. To determine the charge time we first determine the Mah rating of the cells. You should ALWAYS use identical cells in a battery pack. A good charge rate would be equal to 1/10 "C". If I use 2500 Mah cells, my chargers output should not exceed 250 Mah.
Since electrical pressure builds during the last phase of the charging sequence the resistance factor), the amount of current that the cell accepts slows down. A 20 % overcharge in TIME is considered reasonable without cell damage. The formula for insuring a full charge to 2500 Mah cells would be 250 Mah output for 10 hours to equal 2500 Mah plus 20 % or 12 HOURS of TOTAL charge time.

Another principle that should be brought to light at this time is "Fast Charging"

If you were to increase the amount of current output to the cells, you will charge them quicker. The result will be an initial or TEMPORARY higher voltage within the cell, but at a reduction in the amount of current that the cell will hold. A slower charge will provide the same sustained voltage, but will fill the cell to its rated capacity and then some. This is all due to the RESISTANCE of the cells. For our purposes, "hotshoting" the cells gives no gain for time in the field. The theoretical optimum "average charge rate" would be 1 C, but you will only get this from a more sophisticated charger that can be programmed for the different size and capacity cells.

3. I would consider it a wise investment to have multiple sets of cells in order to balance their use. I have 6 sets of AA cells for two detectors. I have three sets of 8 cells for my Explorer II, and three sets of 4 cells for my Wife's Ace 250. I labeled all of the cells with their respective "group" numbers with a permanent marker. All cell groups are kept together for use and recharge. When I go in the field, I always have a fresh set in the detector, and a fresh spare set just in case. When I return, the spares go into the detector for the next swing session, and the used set gets cycled. Over time, the cells will "match" themselves to one another for a slight performance "boost" if kept in groups.

4. When buying new cells, DO NOT exceed the 1/10 C charge rate for the first 5 uses. These initial chargings are forming the cells to handle their rated capacities. Faster charge will not allow this procedure to occur, thereby limiting the cells to a "short" charge. After the 5 initial uses, faster charge rates can be used.

5. If you are in a hurry, and own a computerized charger such as the one I have, you should not exceed a charge rate of 1.5 C. Small batteries tend to heat up pretty quickly, and you don't want to burn up the cells. I can charge a pack of eight 2500 Mah cells at 1 C (2.5A) in about 40 minutes.

I received my "Masters Degree" in "Battery Science" by being involved in highly competitive radio controlled car racing and electric flight. We were always striving to get that little "extra" to get the edge on competition. In some racing we were restricted to "spec" battery packs and stock motors. The only differences were the driving skills and chassis, battery preparation.

7. If you want something better than the previously mentioned "wall wart", the next level chargers have a switching circuit built into them. They can be of 3 types. The first would be a charger that switches to a trickle mode to maintain battery voltage. This type can be left plugged in without fear of damage to cells for "REASONABLE" time periods of a day or two. The second type switches off when peak voltage is detected. This may cost a little less, but cells do lose their charge when stored. This loss is minimal when we are talking a few days. The third type is a combination of the previous two, where you can switch the functions after initial charge according to your preferences. Some will allow a startup in trickle mode as a "top off" feature. Remember, Nimh's are designed to be topped off at any point. Nicad's must be discharged to at least .6V per cell before recharge or you risk developing the dreaded "memory". A simple way to discharge cells is to make up a set of a few 12 V automotive stop light bulbs wired in parallel. Connect them to your battery pack and run the cells down until the lights go out. It does not hurt to do this with Nimh's every once in a while.

8. The most sophisticated chargers are known as battery "cyclers". These are computerized units which allow for programming of EVERY aspect of the charge, along with being able to handle many sizes, types, capacities, and battery technologies (Lipo, Nimh, Nicad, Lead Acid, Gel Cell). While more expensive, they offer the utmost in versatility. They will not only charge the cells, but discharge, cycle, topoff, and "hotshot". I can recommend the Great Planes "Triton", and the Duratrax Intellipeak "ICE". These units can be had for $120 - $130.00. I have the "ICE", as it is a later technology, and is able to provide graphs of the charging / discharge process on its LCD screen. Both models offer a temperature sensor that will further control the charger function while monitoring the cell temperature. This addition is well worth the extra $10.00. Heat is a cells worst enemy. The "ICE" is also capable of providing stats on the cells performance. Both of these units operate off of 12 V. You can plug them into a vehicle lighter outlet, or clamp to the vehicle battery if out in the bush. For the workbench, I have them connected to a 12 V power supply. An old computer power supply or hobby transformer will work fine.

I know that there are many of you that think rechargeables will not perform like the alkylines. In today's technology that thinking is a thing of the past. The only real difference is the quicker voltage drop off at the end with the rechargeables. The capacities today are almost equal. 5 years ago Nicads were almost the only game in town. 4 years ago the capacities of AA cells maxed out at 800 Mah, today, 3000Mah with only 10% loss over 1 year of storage is now a reality. Tomorrow, Lithium Polymer cells (used in cell phones) with their small size, light weight, and increased voltage will be the norm. We are already using them in Electric model aircraft for flight times as long as 45 minutes, or speeds of 125 + Mph. Put them in a detector, and run it for a week without turning it off.

Hope all of this helps. I will post some pics asap.


WThesing 07-30-2006 03:34 PM

Re: Battery Clinic Chapter Two
1 Attachment(s)
This is the equipment that I use.

WThesing 07-30-2006 03:36 PM

Re: Battery Clinic Chapter Two
1 Attachment(s)
The types of chargers mentioned. Smallest one has an auto shutoff after 14 hours. The Pulsar would be too expensive for what we would use it for. The ICE has more features.

WThesing 07-30-2006 03:37 PM

Re: Battery Clinic Chapter Two
1 Attachment(s)
Set up and charging. I purchased two cell holders from Radio Shack. One hold 4 the other 8. Slight modification (added plug) to connect to charger/cycler.

WThesing 07-30-2006 03:44 PM

Battery Clinic follow up & Questions
I thought I'd lock the two chapters in case of addition/modification, and to keep them clean. We can start this thread if there should be any comment, criticism, question, or pats on the back. :lol:

Moderator Note: For simplicity, I merged the two chapters of the Battery Clinic into a single thread and left it locked.

DougF 07-30-2006 09:08 PM

Re: Battery Clinic follow up & Questions
Thanks for posting this - a lot of information, much of it new to me. I have a Kodak charger which came with a digital camera, and plan to buy NiMH batteries for the detector. Thanks again.

ToddB64 07-31-2006 12:40 AM

Re: Battery Clinic follow up & Questions

Originally Posted by WThesing
I thought I'd lock the two chapters in case of addition/modification, and to keep them clean. We can start this thread if there should be any comment, criticism, question, or pats on the back. :lol:

Bill...........I'll start with a pat on the back.....nice work !! :D.

I may have further comments/questions after thoroughly digesting both chapters.

BTW, your entries were timely for me, as I had a Post.It note stuck on my desk to find out more about "Mah".

Thanks for the help !


WThesing 07-31-2006 06:41 AM

Re: Battery Clinic follow up & Questions
It goes without saying.........Yer all welcome!!!! :lol:

ToddB64 07-31-2006 11:00 PM

Re: Battery Clinic follow up & Questions
Hi Bill !! :grin:

When I bought! my Ace250 detector, the dealer suggested two accessories, i.e. a coil cover and a
battery charger.! The charger he sold me is a China-made Ni-MH Fast Charger, that will take two or four
AA or AAA batteries. The charger has a red LED for batteries no. 1-2, another red LED for batteries
3-4 and a green LED marked "Fast/Trickle". The charger came from the manufacturer loaded with four
AA, 1800 mAh batteries and is still unused, as I am running the Ace with "Energizer" AA's no.E91,
2850 mAh batteries currently. The charger INPUT requirements are: 120 Volts AC, 60 Hz, 10 W, and the OUTPUT is expressed as: 2x(2.9V = 300mA Max). NOTE, the equal sign was all I had available on
my keyboard and it should be the symbol for direct current, i.e. a solid line with a parallel dash line under
it. The instructions that came with the charger state 3 warnings: "Do not charge any Ni-Cd or Ni-Mh
batteries with a capacity smaller than the battery chart. Always disconnect the charger from the AC outlet and/or remove the batteries when the charging cycle is completed.This charger is NOT intended for the batteries to be trickle charged for an extended period of time once the fast charging cycle has been completed." The battery chart mentioned, shows 1300mAh as the minimum for AA! Ni-MH's.
There is also an example in the instructions regarding charging time that states "Charging time for
1600 mAH! AA! battery is approx. 5-hours".

Now, I have some concerns/questions, as follows:

#1) First of all, I'm not sure how to interpret the designated charger OUTPUT . It looks like a mathematical formula. Does the OUTPUT vary with the load demand, depending on battery size, mAH
rating and number of batteries being charged ?
#2) The mAH rating (1800) of the batteries that came with the charger do meet the manufacturer's
chart minimum capacity, but according to your suggested 1/10, the charger OUTPUT should not exceed 180mA. Will the charger "fry" the batteries that came with it ?
#3) Regarding the charging time example given above, would I be correct to figure on 5.625 hours for
the 1800mAH batteries ?! ( 5/1600) x 1800 = 5.625!

My formal education is HS + 1yr Evening College (Math & Psychology) + Home Study Course in Basic
electricity, atomic theory, etc. + self taught Trig and some other areas of science! that have interested me over the last 45 years ( I am now 65 yrs. young !! ;)! ).

I really appreciate you taking the time to educate everyone on this interesting subject !

Thanks much Bill !


Vlad 07-31-2006 11:21 PM

Re: Battery Clinic Chapter One
Very well written article Bill, cleared the Mah part for me.

Thank you for taking the time!

WThesing 08-01-2006 09:01 AM

Re: Battery Clinic follow up & Questions
First off you have me beat by a mile in formal education. I am a high school grad that is self taught in a lot of "interesting " things. I am by no means an electrical engineer, but a graduate of the Univ. of Saigon. I will try to answer your questions. :grin:

1. It is quite possible that your charger has a computer chip that would enable a variable charge rate. The amp load will diminish as increased resistance is detected. There are algorythms programmed into the chips to provide the best AVERAGE charge for a range of cell capacities. Once reduced below 1/10th C, it would then be considered a trickel charge.

2. No. Since it seems that you have a more advanced charger, I wouldn't worry about it, although it is possible that its design does not allow for OPTIMUM cell formation in the initial first charge cycles. I provided the info in the article as a guide for the most common and basic chargers that are sold, as well as a charge rate for those who may have a programmable charger available. The other type of sensor that may be in your unit could be a simple temperature sensor,although I doubt it, that backs down the charge rate as the cell temp increases thru resistance.
3. Your formula would be correct. I always use percentage multiplied by time, where a time constant is provided.
4. For the purposes of detector use, we do not have to be as exact in trying to cram the maximum bit of juice into the cells. Our only concern is to not destroy the cells by over stressing them. There is a "corridor" in which we should stay that has a "fudge factor". The difference in performance would be too small to be of concern. Hope this helps.


SteveMN 08-01-2006 09:29 AM

Re: Battery Clinic follow up & Questions
Bill, Thanks for the very informative and well written lessons on rechargeables. I know you shed some new light on this subject for more than a few of us. Keep up the good work!

rcasi44 08-01-2006 03:40 PM

Re: Battery Clinic follow up & Questions
If I understand what Todd was trying to write the charger output is 2x 2.9v (2.9v for battery 1&2 and 2.9v for batteries 3&4)(2 batteries at approx. 1.4V each = 2.9V). I don't know if each battery is charged at 300ma or if the total ma supplied is 300ma max. My quess is it can handle 300ma Max.

capacity= (1.4v+1.4v) (1.4v+1.4V) charged at a total max of 300ma rate. Rob

WThesing 08-01-2006 04:33 PM

Re: Battery Clinic follow up & Questions
The charger in question has TWO seperate charging circuits TOTALING 300 Ma.
150 Ma per bank.

ToddB64 08-03-2006 11:05 PM

Re: Battery Clinic follow up & Questions
Thanks Bill/THesing and Rob/rcasi44 for your help !! !:D

I'll be sharing all of the info. with my youngest son Gary. He is a professional computer programmer and has decided
to try his hand at building a model robot of some sort, with servo's and battery powered. He is in the "thinking
about it " stage and I think he will find your posts interesting and informative !


WThesing 08-04-2006 07:35 AM

Re: Battery Clinic follow up & Questions
He should have an easy time of it. With racing R/C cars, we have to consider the endurance factor of a race as well as staying under weight restrictions. With electric R/C flight, weight and balance are HUGE factors, as well as the power to sustain the load and provide performance for a decent period of time. If weight is a factor, consider Lithium Polymer cells. They are expensive, but well worth the investment. Standard voltage is 3.7V per cell. Sold as 1S, 2S (7.4V), 3S (11.1V), and 4S (14.8V). Amperage goes as high as 60A. I am flying a Tigermoth 400 (Biplane with 38"wingspan) on single 2S packs and getting 25 minute flight times on average with a performance propellor and doing aerobatics.

ToddB64 08-06-2006 04:16 PM

Re: Battery Clinic follow up & Questions

Originally Posted by WThesing
He should have an easy time of it. With racing R/C cars, we have to consider the endurance factor of a race as well as staying under weight restrictions. With electric R/C flight, weight and balance are HUGE factors, as well as the power to sustain the load and provide performance for a decent period of time. If weight is a factor, consider Lithium Polymer cells. They are expensive, but well worth the investment. Standard voltage is 3.7V per cell. Sold as 1S, 2S (7.4V), 3S (11.1V), and 4S (14.8V). Amperage goes as high as 60A. I am flying a Tigermoth 400 (Biplane with 38"wingspan) on! single 2S packs and getting 25 minute flight times on average with a performance propellor and doing aerobatics.

Thanks again Bill/Thesing ! :grin:

I'll pass this info. along to Gary.........I'm sure he will find it useful.


ROF 08-10-2006 10:37 AM

Re: Battery Clinic follow up & Questions
EXCELLENT posts and nicely detailed.
I have read and studied this subject over the years but your posts have compiled the most important aspects without being overly detailed/confusing.

I use Energizer 2500mHh batteries. Was using the Kodak photo cells that lasted forever it seemed. My current chargers do switch over to trickle charge after they are fully charged. I too have them marked or labeled into groups which makes keeping track of their use cycle easier. I'm an old telecomm engineer so sometimes I get carried away with details - LOL.

You briefly touched on the topic of "memory". This is very true with this type of battery. I always "fully" discharge before I begin a recharge cycle. This prolongs overall battery life and assures a longer life cycle before the voltage drop off occurs during use. My chargers do not have a discharge feature now (the one that did has died) so I I connect them to a load (a small penlight flashlight can be used if necessary) to fully discharge them.

My only point is that the memory factor should be noted. It probably isn't good practice to just toss them into a charger after a brief stent into the field. Run them down first, then recharge. This will greatly improve their useful life.

Thanks again for a great post and excellent topic.

Brian 08-10-2006 12:59 PM

Re: Battery Clinic follow up & Questions
Memory effect is an urban do get voltage depression but its effect of overcharging caused by cheap domestic chargers. If you don't over charge then there's no need to fully discharge which reduces the amount of recharging cycles you can do and risks reversal of the cell.

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