Ron, good idea. I had already done this before on my GT to determine when the low battery alarm kicks in and it's right around 10.2V. This was also tested with a high amp able lipo, so there is no worries of voltage sag after the load (detector) is taken off the battery which could possibly cause the voltage to sag under load. BUT, I don't think that is an issue with a good battery pack (rechargeable nimhs or regular batteries) either, because especially nimhs and nicads are able to hold up under much higher amp draws than the roughly 50 to 60ma that the Sovereign consumes. And I believe the high end of that amp draw from memory is only around 60ma but at tops like maybe .69ma (when using headphones, as the internal speaker might draw a bit more). So, there shouldn't be any issues with a false voltage reading of the pack from bouncing back up in voltage after the load (sovereign) is taken off the battery. Same deal with regular non-rechargeable AAs. They are more than capable of handling much higher amp draws than the 50 to 60ma of a Sovereign or Excalibur.
I was careful about correctly measuring the low voltage cut off point for the low battery alarm because lipos should never be drained passed 3V per cell, or 9v for a 3 cell series lipo, or it could ruin the battery. So I made deadly sure there was no risk of draining lower than 9V and checked several times once LVC (low voltage cutoff) was hit with several different packs, both lipos, the stock rechargeable, and by using regular AAs in the alkaline holder, so I'm very confident of that. Lacking some odd exception to the rule, i would figure all Sovereign and Excal models should be right around that range for the low battery alarm. I believe from memory Kered said his Sovereign (don't remember which one) cut off at about 9.8V and would sound the low battery alarm then. That's well within the tolerance variations of a voltage regulator. No two are going to be perfectly the same exact voltage #, but it probably wouldn't vary by more than say around half a volt or so at the most as two when the low battery alarm kicks in.
The only exception here is a bad pack. If it has a bad cell, even under the super low amp draw of the detector it's possible the voltage would sag under load and then bounce back up after removing it from the Sovereign and reading it with a volt meter. That's also what is known as surface charge or "surface voltage", which can happen with a bad cell, but is much more common under much higher amp draws then metal detectors use.
I see from Kered's quotes that I posted than he had indeed run 8AA nimhs in both his GT, Elite, XS2, and in fact even in his Excalibur alkaline battery pod. If you read his quotes closely you'll see him make reference to the POD, meaning on his Excalibur, and reported no issues with short run times.
[size=x-large]I've got a few more quick points. IF you are only getting short run times out of 8AA nimhs in the alkaline holder of your Sovereign or your Excalibur, IMO it's due to one of the following issues...[/size]
1) You are not using 2500ma or higher nimhs to insure the voltage stays high via the high capacity during the discharge cycle. Shoot for the highest capacity you can find because the higher the capacity the longer the run times.
2) The cells you are using are either of poor quality or have been used and abused, and so they are not charging to full capacity.
3) The cells you are using are once again of poor quality or have been used and abused, so even if they are charging to capacity they are not reaching as high of a voltage as they should.
4) The charger you are using is not charging correctly. It's either shutting off too soon (some do this), or it's only charging to a target voltage of 1.2V (or maybe even lower) per cell and then shutting off. Even most cheap chargers won't do this though and instead use the most common/best method described below. Some cheap chargers, although rare, do determine the the pack is charged this way. You want to use a "delta peak charger", which most are (even most of the cheap ones), so as to insure the pack is determined to be charged by way of the m/v threshold trigger of the charger (which you don't need to worry about setting on most consumer chargers), and so the pack is reaching full potential in both voltage and capacity by this proper charging method. In that instance the pack will not stop at 1.2V, nor at the capacity on the label of the cell, but rather when the voltage begins to drop steadily, which is the signal the pack has reached it's peak charging condition. Most charges use this method but some don't, and others have too low of a m/v setting built into them that can't be changed, so the pack is false peaking perhaps. During the charging process it's normal for the voltage to dip a little here and there as it climbs. If the m/v threshold setting on a cheap charger is calibrated too low at the factory, then it is falsely thinking the slight voltage drop it's seeing means the pack has peaked when in fact it's just a little dip on it's way of rising more to full charge. You don't need to worry about this with most consumer chargers as it's already set to a good number, and that's why it's risky to play with that setting on a charger that allows you (more advanced ones), because set too low the pack falsely terminates the charge. Set too high and the charger never knows when to stop. I normaly set this to 5 to 7 m/v when charging nimhs, and 12 to 14 m/v when charging nicads, because nicads dip more in voltage when charging and also drop more in voltage when done. Stick nimh batteries in a charger designed for nicads and you can see the risk. The charger never sees the peak and overcharges the battery, risking a fire.
5) To insure you reach full voltage and capacity potential, that's why it's important to use a charger that will determine when full peak has been reached, and will clearly signal that the pack is done charging. Stay away from chargers that don't clearly signal the end of charge or only tell you to put the pack on for X amount of hours, because those types of charges probably have no way of determing when charge is complete and just constantly put out a trickle charge (sound familar? as in many stock detector chargers). With a "charger" (meaning just a wall transformer) that does this constant trickle, in reality it doesn't matter if it's plugged into a nimh or a nicad, because it's just putting out a constant low am trickle charge. With no way to determine the pack has peaked, the low trickle charge rate insures the pack won't be damaged by still being fed a charge when it's peaked. This is OK with nicads but I always read will slowly destroy nimhs. For that reason, if you are putting a nimh pack on a constant trickle "charger" (wall transformer) and leave it on like that all the time, over time the capacity of that pack is going to continue to degrade. For that reason, if you are using one of those nimh high capacity aftermarket packets on your stock wall transformer, you need to pay extra attention to how long you leave it on there. Use the math...1600ma pack (most of them are that I saw for the Excal)..Excal consumers roughly 50 to 60ma per hour (round it off to 100ma to be safe). You hunt 5 hours. You've drained a max of 500ma out of a fully charged pack. Let's say your wall transformer puts out 100ma. That means about 5 hours to fully charge again. I'd overshoot the # by an hour or so because charging is inefficent and so takes in general longer to put the lost capacity back in.
6) You are not using low self-discharge nimhs. So you charged them several days ago and they have already self discharged on the shelf. If you are using regular nimhs and it's been say a week or two then for sure you need to re-peak the pack before going out. Some are better than others at not draining on the shelf. But if you don't want to charge before every hunt to insure you don't hit that low battery alarm, then for sure buy low self-discharge nimhs. Some are very good these days and will hold their charge for months without needing re-peaked.
That's all I think I've got to say on the whole subject. Can't make it any more clear than I have, or to explain the possible problems above where some say they are only getting very short run times. If you follow those 6 rules above when shopping for, charging, and using nimhs, I'll be shocked if you don't get the run times Kered was reporting. I remember him saying to that he didn't even re-peak his packs between hunts and was getting longer run times than the stock 1000ma 10 cell pack with his 8 cell nimhs, but I think he said he was using low self-discharge nimhs so they wouldn't sag in voltage between hunts. I'd get low discharge nimhs, but you must research them because some do not hold up to their claims. Many tests out there on all these cells by guys who are as avid about their batteries as I am, and they made it their business to test all these low self-discharge nimhs to see just how well they compared to each other.
Final point- If you don't get low self-discharge nimhs and you don't re-peak your pack say the morning of the hunt, you are risking the low battery alarm IMO. Although some normal (non-low self discharge nimhs) are better at holding their charge on the shelf than others, so you may very well be able to go weeks if not a few months without needing to re-peak. But just the same, if you want to have confidence in that then buy the low self-discharge type nimhs. If you don't, plan on re-peaking before each hunt, or at the very least every week to perhaps every month or so between infrequent hunts. With low self-discharge ones though for sure these days they can sit for months without needing re-peaked. I use a 3 cell lipo, which has just about zero self discharge on the shelf. Charged up, I can let a pack like this sit for a year and it's still completely charged for all intensive purposes. That's just one of the things I love about lipos.
) here's a few quick points- Did you charge those cells right before you went out or at least within a day or so? If not they probably had already self discharged a lot and thus hardly any run time. That's (besides the super low capacity) is why IMO Minelab put 10 cells in the holder to boost the voltage. Otherwise they'd have a lot of unhappy customers who charge the pack and it won't give the machine any kind of run time after it's sat on the shelf for a few days to a few weeks or so. By wiring 10 cells in series they are increasing the voltage of the pack, making up for the low capacity/faster draining of those low capacity cells and also gaurding against voltage sag due to self-discharge on the shelf. The cut off point for the low voltage input of the Sovereign's regulator is a bit higher than found on most other detectors, and that's why others only use 8 cells with their low capacity stock packs.