Proprietary NiMH battery query.

The Garmin battery I refer to is the one at the bottom of this post.

First question is that I have a hand held GPS that normally takes two AA batteries, or the special Garmin battery. I am assuming that the Garmin battery is more than just two AA's strapped together, possibly with some extra circuitry.

My first question is if this unit runs on 2.4V which is what a pair of NiMH batteries put out, then how is it that it can not be harmed by a 5 Volt usb outlet. Does this mean that the GPS unit itself would have a resistor or something that knocks the voltage down further. Garmin did say to me that anything more than 5V could fry it.

Apparently if I use a pair of rechargeable batteries in it then it will not charge these batteries if it's plugged into the bike usb outlet, but Garmin thought that it "should" charge their special Garmin battery while the unit is running off bike power, but they weren't sure. Does this sound like it would be because it needs some extra circuitry which is what would be in the Garmin battery?

My guess (emphasis on guess) would be that the batteries are pretty plain. Do you have a picture of the battery compartment? It's not at all impossible that there's something there that allows the device to notice the difference between this pack, and standalone AAs.

It looks like two plain AA batteries. The charging can be controlled from a switch that the plastic around the batteries activate.

Awright, well spotted guys, at first I was looking at the connectors and it all looks normal, then I spotted this little rubber bit which I at first thought was just to put pressure on the batteries to keep everything snug, but I took a battery out and I can see that the little round rubber bit at the bottom does not in fact contact the batteries, so this may very well be the switch you refer to.

Looks like it's going to be another 30 minute wait on the phone to talk to Garmin again, because if that is a switch then prolly a bit of cardboard pressing on it is all I need to get it to recharge my normal rechargeable batteries.

user11 said:

Awright, well spotted guys, at first I was looking at the connectors and it all looks normal, then I spotted this little rubber bit which I at first thought was just to put pressure on the batteries to keep everything snug, but I took a battery out and I can see that the little round rubber bit at the bottom does not in fact contact the batteries, so this may very well be the switch you refer to.

Looks like it's going to be another 30 minute wait on the phone to talk to Garmin again, because if that is a switch then prolly a bit of cardboard pressing on it is all I need to get it to recharge my normal rechargeable batteries.

Click to expand...

You are right, this button in the middle between the batteries IS the charging enabling switch. All you need is to place some stiff thin metal card (plastic one might be not strong enough and will bend) to be able to charge any pair of NiMH cells inside a Garmin device. Of course, they must be of the same model, make and manufacturing date.

But I personally charge those in a dedicated charger. Just not worth the effort

OK thanks for that reply, first let me say that the reason I want to do this that I use this on my motorbike connected to a 5W usb outlet connected directly to the battery with an inline fuse. So it will usually be plugged into the bike and then when I get off and take it will me it will always be fully charged. It's slightly annoying to unplug and replug the device into the mini jack every time I disembark so often I'll just let it run on batteries and if I'm going for a longer ride I'll plug it into power, so I never really have to bother about getting stuck or thinking about the batteries.

I tried it and it all works but there's some funny business going on and I'm now trying to work out what is causing this. Garmin is not much use because they just robotically parrot that they don't recommend anyone else's batteries be recharged, but parsing that what they are really saying is that they know that eventually someone is going to put ordinary batteries in with the plastic and explode the batteries. So they are just playing it safe.

Now all would be good except for some strange behaviour and I am guessing that it may possibly be due to voltage. OK this is what happened I let the batteries charge up fully in the unit, unplugged it then checked the battery voltage with was 14.4 which seems pretty high for NiMH batteries, but I'm told that they quickly drop down to 1.2 and stay there. FFIW, I have found this to not be the case, I put two sets of batteries in two units today, and etrex20x and the oregon, the etrex had Everready 2000mAh rechargeable, which I think are LSD, and the the oregon had the panasonic pro 2400mAH eneloops. I ran them in both units and for an hour with lighting on and when I got back and checked they were down to 13V and 13.5V respectively. Is this normal now for good quality eneloops? I mean these are old batteries but they seem to hold a decent charge for a decent time. They are charged in a good quality Powerex charger so they are never cooked.

Anyhoo, so after I unplugged the Oregon and checked the Voltage at 14.4V I put the batteries back in with the cardboard and was going to put it back on the bike, but the Oregon would not start up. I opened it up took the cardboard out and put the batteries in it still wouldn't start. I plugged it into a little hand held power supply, (which is in fact what I used to charge the batteries in the Oregon just to be safer) and it started up. When I put the batteries in again, it started up. So I put the cardboard back in and it would not start.

OK I went through this procedure a few times but then it would not even start up from the external power supply. After a few minutes it did start again. But it won't start up with the cardboard in. OK I'm sort of suspecting that this has something to do with the high voltage of 14.4, which isn't really high but it's high for NiMH. Later in the day, after running the batteries down to 13V I put them back in with the cardboard and it did boot up no problem. This makes me more convinced that it could be the Voltage but that could just be a coincidence.

Now here's some more very strange stuff. I put a Fluke 101 meter, cheap but reliable, and I have a high degree of confidence in the Fluke as it reads the same as the voltage on the Powerex. Ok I plugged the Oregon into my little usb power supply which probably puts out about 0.5A and holds about 4Ah of stuff, without any batteries in and no rubber switch pressed down, and I was getting a voltage reading of 2.2V from the +ve to -ve terminals on the right hand side, and very very strangely I also got a similar reading when I read across the two +ve terminals, the one on the top right and the bottom left. This has left me mystified and confused. Pressing the button while checking this again made no difference.

Just for reference I did the same thing with the eTrex and it has no voltage across any terminals when plugged into the external power brick.

I do not know what to make of all this. Oh also note that the photo in the top picture says 2000mAh and 2.4V, which looks like the total voltage for the pair and the single capacity for the battery. Which sort of doesn't make sense, unless these are two 1000mAh batteries but then they wouldn't last 16 hours. It's not possible or is it that these batteries are in fact 2.4V each, for a total of 4.8V surely? especially as it takes normal batteries.

vadimax said:

You are right, this button in the middle between the batteries IS the charging enabling switch. All you need is to place some stiff thin metal card (plastic one might be not strong enough and will bend) to be able to charge any pair of NiMH cells inside a Garmin device. Of course, they must be of the same model, make and manufacturing date.

But I personally charge those in a dedicated charger. Just not worth the effort

Click to expand...

Please stop putting batteries with that high voltage into expensive electronics, at least until you figure out what'a going on. ;-)

Also, are you sure these are NiMHs?
And what's normal charge time for the Garmin?

The reason I'm asking about normal charge time is that some chargers work at a constant trickle charge, low enough to not damage normal NiMHs, but the LSDs are more sensitive to overcharge.

Hi, not sure what you mean by that high voltage, they are just normal AA eneloops that I'm using which is recommended by Garmin, it's the Garmin battery that I am not using that has 2.4V and 2000mAh but that just doesn't make sense they must mean 1.2each surely, I do know that when charged in the GPS, Garmin says the battery pack takes 16hours to recharge, but the batteries are designed to be unclipped and put in a normal charger.

So maybe then I'll get a pair of non LSD 2000 man batteries. What I don't understand though is if the unit is designed to also take normal alkaline batteries at 1.5V that even if the eneloops got up to 1.45 that shouldn't be a problem should it?

Also what do you make of being able to get a 2.2 voltage across the pos and neg terminals without the button pressed, only on the Oregon but not the eTrex? And stranger still I get almost the same reading going from pos to pos which you'd think would not make a circuit! I'm confused as hell. I haven't tried charging them on the bike yet and I won't be doing that till I am sure that it's OK. But it looks like non eneloops might be the solution.

I have found what might be a bit of a clue in the setup the eTrex has battery setting options of Alkaline, lithium or Rechargeable NiMH, however the Oregon has Alkaline, Lithium, NiMH and Precharged NiMH. So by 'precharged I assume that means LSD. Garmin are not clear about this at all because they don't say how to set it for their battery pack.

I think what terjee is talking about is that you have apparently misplaced the decimal point in most of the voltages you have presented. I believe when you type 14.4 you meant 1.44, which by the way is the voltage to be expected from a freshly charged NiMH cell. And I don't believe having to NiMH cells at 1.44v, for a combined voltage of 2.88v is a problem, because two fresh regular non-rechargeable AA cells will present 3.0v for at least a little while.

My suggestion - just put things back together with a normal set of AA cells or the Garmin battery pack, and let the problem just simmer in the back of your mind for a day or so. Then start your testing again, keeping very good notes on everything. I have found this helps me when I just can't figure out what is going on. Let us know how things turn out.

Packs are rated for the pack, not the individual cells, so a pack of two 1.2V batteries in series, 1000mAh each, would become a 2.4V 1000mAh battery pack. Had they been in parallel, it would be a 1.2V 2000mAh pack.

By the high voltage, I was thinking of this:
"OK this is what happened I let the batteries charge up fully in the unit, unplugged it then checked the battery voltage with was 14.4 which seems pretty high for NiMH batteries"

If you somehow got the batteries to 14.4 without them dropping down almost instantly after disconnect, I would be careful about what you put the batteries in. It's a high enough voltage to damage things. Seems really weird if they're able to maintain that voltage though, shouldn't be possible.

Could it be a typo, and be 1.44V?

Or maybe I misread or misunderstood something?

Whoops! ha, my bad, sorry about that, yes a decimal typo. thanks terjee and timothy. Sorry for the confusion. Just to clarify, I don't have the Garmin battery pack, because it's $35 for a pair of what looks like 1Ah batteries but then how could they power the unit for the same time as a pair of Alkalines? I'm guessing that surely must be a mistake.

After further delving into this apparently this is a common thing to do, use normal rechargeable batteries and put a bit of something to hold the button down.

What do you guys think about being able to read voltage at the vacant battery terminals when it's plugged into an external battery pack on the Oregon but not the eTrex? This is without the button pressed in? I'll have to I think compose myself as you suggest and then plan some questions for Garmin and hope they deign to answer me. Maybe I'll try some freshly charged eneloops and some half run down eneloops after I think about this some more. Thanks for you answers. But I would be interested to know your opinion on what it means to find voltage at the vacant terminals.

Please pay attention that Garmin devices have battery type selector in their firmware. You need to charge your cells (they will be around 1.45V) and then set "NiMH Precharged". Otherwise you will get wrong leftover charge indication.

If you insert half-charged NiMH batteries (1.2V) you should select "NiMH".

Measuring circuits with a multimeter can often be confusing, because you're looking at just one point of a possibly quite complex system. Imagine this for example:

You connect a battery. The device has capacitors between the battery and internal voltage regulator (almost guaranteed). Those caps are now charged by the battery. You remove the battery, then measure. Voltage could still be present, from the charged caps, even with no power connected at all.

Often measuring in such off-states can give random-looking results like this.

As for difference between devices when external power is attached, it's similar. One device might ground the battery terminals, another might connect the output of your power supply to one of the battery terminals when using external power, and so on.

Based on the 2.4V specification, it's most likely in series.
Each cell would be 2000mah due to series.
If you say they're 1000mah, that would make it 1.2v only in parallel.

Late into this thread - I have a few Garmin handheld GPS units, including the Oregon.

There is nothing fancy about the Garmin battery pack. Its main function is to depress the button on the circuit board that enables the charging process (and disables the manual menu selection for battery type). In fact the battery pack you linked is an after market version of the Garmin 010-11874-00 battery pack.

About 3 or 4 years back when I first got the Garmin Oregon 600, I cut out an old credit card sized plastic rectangle and put that underneath 2x Eneloop NiMH AAs and that worked fine to charge.

I now use those sim card pop-outs left over from a large size sim card when you pop out the micro or nano sim cards for you phones. They work fine and are easily replaceable (for me at least when I travel and hike overseas).

I have been using Eneloop Pros and now switched to the cheaper Japanese made Ikea Ladda white 2450mAh AAs as they give me longer battery life compared with standard Eneloops.

The simcard plastic sits underneath the Ikea Ladda batteries and enables the charging from the mini-usb socket. I have been doing this for at least 3 years with no issues. These days however, I don't typically charge the batteries in the Garmin Oregon, as the charging is slow.

I only charge using the built-in mini USB cable on the odd occasion now using a Li-ion powerbank. Typically I have a pair charging in an external 2 or 4 slot AA charger via the powerbank in my backpack, and will use the other 2 in the unit for the day.

If you use rechargeable NiMHs without depressing the button in the battery compartment, and then in Setup > System > Battery Type not selecting either Precharged NiMH (for LSD batteries) or NiMH (for other NiMH batteries) and you leave it as Alkaline, the battery indicator will be incorrect and report your batteries are discharged earlier than they actually are.

@Terjee, OK thanks for that heads up on measuring at the terminals.
@Vladimax, I checked all four setting from Lithium to Alkaline and they varied between one and four bars. When using battery power the firmware battery selector disappears. But it still doesn't seem to work well because I had fully charged NiMH batteries in running on battery power with the button pressed down so there is no firmware selection. It started at 4 bars, but very quickly dropped to two after about an hour without using any backlight, then it stayed at two all day and suddenly just turned off. It bypassed 3 bars and it bypassed 1 bar.


@keithy ok thanks that is the reassurance I was looking for. Garmin have not got back to me yet. I mainly got a bit worried when suddenly after charging the batteries in the Oregon it would then not switch on with the button depressed, this happened a few times it eventually switched on after a few minutes. But it all seems fine now.

My reason for wanting to go down this route is that I will mainly be powering of the usb outlet on my motorbike and therefore the batteries will always be charged and when I take it off the bike when I park I can use it at the same time. Slow charging in this case would be a bonus!

However if I may ask when you are charging the batteries in the Oregon and you get the flashing battery symbol, is that symbol supposed to stop when it's fully charged?

You probably won't get any response from Garmin other than the usual "you should not attempt to charge any battery that is not the official Garmin battery". The reason is pretty obvious. They don't want you to charge a non-rechargeable battery in the device, like putting in a non-rechargeable lithium AA or alkaline AA and depressing the battery case button on enable USB charging.

I have taken the original Garmin battery pack apart, and there is nothing special about it. For example, here is a way to take the pack apart, and then charge the individual cells in an external charger.

https://www.youtube.com/watch?v=86Sk8QOUTAI

When you have the battery case button depressed, and you connect a USB power source via the mini USB cable, the battery indicator will show the lightning, and the green bars flash from left to right. When it is full it will stil show the lightning icon, but all the green bars will remain green and no longer flashing. As long as the external USB power source is connected, it will charge the batteries in the unit regardless of whether the Garmin unit is powered on or off.

The behaviour you mentioned about skipping the 3 bars and 1 bar, it might be that whatever you are using to depress the battery case button may not be enough to fully depress it continuously. So the unit detects a lower voltage than expected for default alkaline batteries and shuts off. Or if you use the features that have a high current draw (like the camera/flash on the models with camera), map redraws with the map speed set as "Fast" or checking the Satellite status page. Also if you are running the Barometer logging (pressure trending) as always running (even if the device is powered off, it will still record the barometer pressure trend). These will drain the battery quicker as well. Or you could have dud batteries in the battery pack. You can take them apart and test them in an analyzing battery charger and see if they are charging up to the full 2000mAh or not.

Also, while this is probably not what you want, but if you connect it to your USB power source without a battery, the GPS will function as long as the external USB source provides power. I use this function to swap out batteries when I don't want the track log to be interrupted when out in the field. So theoretically you could use it without AA batteries, as long as you keep it plugged in via the mini USB cable. I think the waterproofness is compromised when you are using the USB cable though.

Note that from recollection, a fully depleted 2000mAh Garmin battery pack took over 10+ hours to charge. I found that for me that was a little too long when using it for long hikes. So I go with an external charger and powerbank option, supported by solar panel when going off grid for longer periods.

I should probably add - from recollection, the Garmin terminated by voltage, detecting just under 3V for the battery pack. What I didn't like so much was that when charging it got hot - the batteries/battery pack was quite warm >50C (122F).

I instead use external chargers like the Xiaomi Zi5 or two of the Olight UC Universal USB Magnetic Charger or the Littokala Li202. I find those charge the AAs quicker, and are not as hot as inside the Garmin unit.

@keithy, yes you are correct I have just found this https://s26.postimg.org/pp0vqs2sp/Oregon_6xx_Charge_Cycle.png

The only issue now that I need to work out is how much energy it's drawing after it shuts off. I'm charging on a bike so the aim is to keep it constantly charged but also so that I can remove it and use it when I get off the bike without having to faff around with batteries. Tested it yesterday with the light on full brightness connected to my bike usb and it ended the day fully charged reading 1.5V so I'm happy with that.