Fire up the coffee pot, you're going to need it...
But hey, don't want to mess with this stuff unless you know what you are doing or risk life, injury, or property or machine...And don't take my advice without finding some on your own to confirm or deny how you might think on various aspects of batteries or chargers...
Good for you in checking into alternative power sources. No reason in the world to use throw away AAs these days. Just a big waste of money and material. And the stock rechargeable pack is a boat anchor with rather low capacity that will sit and self drain being old non-low self discharge nimh technology, where now there are LSD (low self discharge) nimhs at cheap prices in much higher capacity.
Ok...
Got some specific info on those LifePo4 cells, but here's the lead up with some info on them and considerations when picking a battery type for your Sovereign or Excalibur thrown in as well...
Ain't going to mention specific cheap potential source of LifePO4 or other cells or chargers...Since they aren't Findmall sponsors, even though they don't dabble in detector circles so I wouldn't think it would be a problem. Just to be sure, I won't provide links or names. But among RC car/plane sources there are a few with ultra dirt cheap prices. Most guys in RC get their lipos and other batteries and chargers along with motors and other parts from these sources as they are dirt stinking cheap. Often about 1/3rd to 1/4th the price on things than other sites. The very hobby of RC means you live and die by your batteries and chargers, especially for electric planes where not knowing these things might cost you a plane, so in RC circles people tend to be fanatical about their batteries/chargers, like me.
You can get computerized charges with screens and settings (not for the faint of heart and shouldn't be used unless you know what you are doing) for $20. I use one for $20 which requires a 12VDC power source like a car battery or one of their cheap invertors, but I run mine off a converted computer power supply I hacked that I garbage picked and yoked out of a computer. One of the reasons why many RC market targeted chargers run on 12VDC, is because often we open the hoods on our cars or trucks we drove to the field in, and charge our packs as we fly others right there in the field.
This charger I mostly use will do LifePo if I remember right (and I bet LifePo4 types will charge on that and it's just a newer battery chemistry, but read up on it and don't take my word for it). I think it also does A123 and a number of other battery types, besides the Lipos and nimhs and Nicads I use mine for. I haven't paid much attention to what various types mine will do since I stick with the cell types I like, but one mode is for lipos, another for sure lithium ion based cells, another for A123, another mode on it for lead based batteries, two other modes for nimhs or nicads, and a final one for I think another for LifePo.
If you don't care to research and learn how to set up a computer based charger, then for sure buy a simple plug-n-play meant for that battery type and it's capacity size (IE: so it doesn't charge it too fast based on cell size).
Far as LifePo goes, been a while since I read up on those and haven't on these LifePo4 ones yet. I'm completely happy at running a 3 cell series lipo in my GT for extra weight savings over hard shelled batteries and less weight due to other battery factors to. I run a 750ma lipo pack (about $7 from them) in my GT. I could have stuck a much bigger lipo in the alkaline holder but I was shooting for max weight savings on my light weight build. I get at least two very long hunts out of them, and because lipos hold their voltage very high during discharge I seem to get at least as long if not longer run times than the stock 1000ma nimh pack. Besides, my charger displays the capacity put back into the pack and when near dead (just above 9V) when I charge it I get around 1000ma if memory serves.
The GT sounds hit's low battery alarm at around 9.8V or so, so no worries with over draining the lipo past the limit of 3V per cell (9V total for a 3 cell series pack) that could damage it. The other perk to lipos, which I suspect those LifePo4 cells have, is they have about zero self discharge on the shelf, so months later in storage they are ready to rock and roll. There are now low self discharge nimhs too that will do almost as good of job of holding their voltage while in storage.
Now, getting more specifics of your question....A lipo 3 cell series pack at full charge is 12.6V (4.2V per cell)....So you are only pushing an extra .2 (point two) volts with using 4 dummy cells, so I *suspect* you'll be fine. Or, if you are worried about it, often computerized charges can be set to cut off the charge at a set voltage level you pick. Set it for say 12 or 12.5V if you get a charger like that and then you're good.
But either way, voltage regulators in things like detectors that are designed to run off batteries often have a rather wide tolerance of input source voltage range. Say if the regulator outputs a fixed 8V to the circuit board (I would suspect it's either than or 9V...probably 9V...on the GT), the input voltage to the regulator has to be higher than the static output voltage to function, but often they'll accept a rather high input voltage. *perhaps* as high as say 14 or 16 volts maybe, depending on the regulator specs.
I have no idea what the highest input tolerance the regulator in the Sovereign is designed for, so for sure don't take my word on that. All your own risk. But, if I were a betting man, since I've ran 12.6V lipos in my GT for several years now without issue, I doubt anything .2V is going to hurt anything *maybe*. I never really checked, but I suspect off the shelf non-rechargeable AAs might come brand new with a bit higher voltage than 1.5V per cell.
The very reason for regulators is to keep the output voltage static and unchanged for the stability of the device as the battery drains, and also I would suspect many regulators that are meant for some kind of battery input source voltage have a pretty wide tolerance of voltage limits. But the only way to know for sure is to take the GT apart and read the part # on the regulator and look it up on the net to see the voltage window specs on it.
I've dabbled with linear regulators for various projects. One example would be the video system on some of my RC planes. Rather than run the camera or it's live video feed to the ground off it's own power source, I used a regulator with a 3V output to power the camera's required voltage. The plane's power source is a 12.6V lipo. The regulator's upper input voltage limit is rated at 9V. Obviously I'm pushing things here...
But I was given a handfull of these 3V regulators for free, so I figured what's the harm in trying? Specs are meant to be "bent" a little anyway.
Anyway, turns out the regulator, even with a heat sink that was added to it to bleed of the excessive source voltage, still gets rather hot. On the ground it'll shut down on thermal overload in about 4 or 5 minutes if I dink around, but once I get it in the air with the plane the wind blowing by the heat sink, which I've mounted to the side of the plane for air flow, keeps it cool enough to avoid thermal shutdown. When it does shut down, once cooled off it'll work again, but thermal overloads are meant to be a safety and not to be relied on, so often they have a very limited life span of trips. Point being,
*IF* your lucky and you over load the regulator being it's ability to bleed off heat, it might have a thermal overload and once cool work again. Big risk though.
Not even sure if these detectors have linear regulators. They might be switching types, which don't bleed off excessive voltage as heat, but rather they pulse the output to keep the output voltage static. Only reason I doubt such types would be used in a detector is the pulsing nature makes them generate a ton of on board circuit noise. You can get around that with the proper added components to quiet them down, but even then I would have to think it would still do some serious damage to the stability (or ability to raise the sensitivity, meaning gain, of the received signal) and cost you a good bit of performance.
Here, dug this up on LifePO4 cells...
"Most LiFePO4 cells operate within a normal or 'nominal' voltage of 3.0 to 3.3 volts, have a maximum operating voltage of around 4.1 to 4.2 volts and a minimum operating voltage of 2.1 to 2.5 volts. Typically a LiFePO4 cell is fully charged at 3.65 - 3.7 volts. In order to get the proper voltage to charge your LiFePO4 battery pack you would multiply 3.65 x the number cells in series. So a 12V nominal pack (3.0V x 4 cells) would have a charging voltage of 14.6V."
For sure I'd wont a charger with the ability to set the max charge voltage per cell. And also, if I'm reading this right...at the minimum of say 9.8 volts (roughly) for the low battery alarm on the Sovereign/Excalibur, then that's 2.45V per cell they'll be drained to (meaning 4 cells with 4 dummies) in the machine when it hits LVC (low voltage cut off of the regulator). Since they are stating minimum operating range of 2.1 to 2.5V per cell, I would suspect you'd have no issues with over draining them and hurting their life span. Seems spot on as a match with the low battery alarm for the GT.
Hope this helps. Good luck, and also keep us informed on the results if you should decide to go with these cells. While shopping around, I'd also look into other new lithium based cell types. Various types have various perks. I just use lipos in my RC planes, so I figure what the heck, I'll use them in my GT light weight shaft build to drop a few more ounces. My alkaline holder with the 750ma 3 cell sitting inside, which just plugs into a small plug I soldered into the holder, so I can still uses 8AAs if I ever want to for some insane reason by just moving the tiny plug out of the way. The alkaline holder with the lipo in it weighs exactly half the weight of the stock rechargeable pack that came with my GT. And that thing is heavy, so there is a big weight savings there.
[size=x-large]Important Reminder: Charging or using any battery type is a risk.[/size] But just like handling gasoline to pump into your car or fill a law mower, the risk can be greatly limited by proper respect and knowledge. Only charge a battery in a fire proof location such as in the middle of a cement floor far away from things that could catch on fire incase it ignites or explodes. Some people clay flower pots over their batteries while charging. The drain hole on the bottom (and now top with it flipped upside down) of the flower pot will allow air to escape without blowing the pot off in the event of something bad.
Make sure you read up and know how to use a charger if it's not a simple plug-n-play design meant to work with those particular cells at that particular capacity (which means proper charge rate for proper cell size is not exceeded).
Lipos back in the day several years back when they first became popular, lacked a balance plug on them and so did the chargers, which meant one cell would overcharge the limit of 4.2V per cell. The result was often a fire. These days all lipos and lipo chargers have balance ports, so each cell is watched in parallel to the battery circuit (pack) and can be terminated from the charge when it peaks 4.2V. As far as over draining a lipo, I have done so by accident (planes stuck in a tree or such).
The only real risk that I know of is destroying the chemistry, but not a fire risk I have never heard anyway. In fact, the last time I read up on the proper way to dispose of them you were to drain them dead with a car tail light bulb or something and then cut the two battery leads (one at a time so as not to short them!) and then throw it into a bucket of salt water for several days to insure it's drained completely before disposal.
But again, don't take my word for it. I don't claim to be right so confirm any advice I give on your own. There are very differing opinions on the care of rechargeables out there. I just go by what I've read, been told, and have learned for myself from years of personal use. Any death, destruction, fire, ruining your detector, or ripping a hole in the universe and changing life as we know it is all on you.
Battery Care For Long Life- Don't charge higher than rated to handle, and even slower insures long life better. Store batteries in a fire proof box. I prefer a metal box with the inside painted with non-metalic paint to avoid a short. The lid should be vented a bit with small drill holes to let any air escape should a battery suddenly vent rapidly fast, which might otherwise blow off the lid. I store my batteries in individual compartments via drywall (non-flamable) that I cut up to make chambers in the box. This way should one go nuclear, it might not take the others with it.
The box is then stored in the refrigerator along with any batteries inside it I don't plan to use for months. This is to help retain their capacity over time (not the current charge, but rather the amount of charge the battery can hold over time with use). My charger will put my lipos to a "sleep charge" that is also meant for long term storage. This voltage level has been determined to best best for retaining capacity over a long storage for a longer lifespan of use. Not sure if those LifePo4 cells have a desired sleep charge so look that up for yourself if you intend to store for long periods of time.
Yea, I may sound overly cautious, but just like you don't smoke or burn "love candles" around you when handling gasoline, some simple steps of common sense that have made handling gasoline for a car or yard equipment makes it not "safe", but rather not all that much "risk", if you know what I mean. Same deal with rechargeables.
So OK then, if that novel of a post don't help some, then better buy a book on the subject.
Good luck...
