Two questions with midland two way radios GTX 1000

[cheaperrooter]

I recently upgraded to AA rechargeable 2100 MAH. It takes 4 of those or can use alkaline as well. First question is when the radios go dead and I go to recharge the batteries (3 units) only one of the four batteries for each single two way radio is dead the other 3 are showing good. Because it happened on all three radios I am assuming this is normal??? Is that normal for rechargeable??? I either won the dead battery lottery or I'm confused about principle because I thought they all drained equally.

The factory 700 MAH pack actually has five AAA batteries for a total of six volts. Alkaline would be 4 at 1.5 or also six. Rechargeable's are only 1.2×4 or 4.8

Everybody is saying that since the radio was designed for 6 V that rechargeables will last longer but no way to get maximum power with only 4.8. A lot of people chimed in with for greater knowledge than I have. Knew what they were talking about and there were many different people.

However I disputed everything they all said with the following statement and want to know if I'm thinking correctly? Everything I learned I learned here

I stated that is not true because even though Alkaline are 1.5, those 6 V are not consistent and will gradually drop to 1.2 V eventually, 4.8 V. However the rechargeable's are consistent and will maintain voltage output until the very end and then drop extremely rapidly and I think the engineers who designed the radio are very much aware of that fact. So in essence the rechargeable AA's with only 4.8 is better than all of them because it will stay 4.8 after the alkaline drop well below that. And I'm sure the radio was designed for maximum output at less than six voltage as it would not maintain that for long.

I was very proud of myself for disputing the experts, and felt like a true member of this forum. Still, I just want to make sure I haven't spouted something that was ridiculously stupid, giving me time to go back and delete before someone labels me a battery moron

 

[cheaperrooter]

No one knows or is it Easter and everyone is out doing fun things but me?

 

[PacificMoon]

I think it is possible the radio detects whether it is being used with 4 AAs or the NiMH battery pack and that it goes into different modes using different boost/buck circuitry depending on that. The user manual specifically says 4 alkaline AAs and it already comes with a rechargeable option. I just do not think it was designed to be used with 4 NiMH AAs. However, I think you are right that alkalines drop lower, although I think NiMH AAs will drop a bit below 1.2 V as well, and that therefore theoretically it could have been made to work with 4 NiMH AAs if the designers wanted it to. I believe that if 4 NiMH AAs work at all, it is very much possible that it will not operate at full power because of what I said earlier. I think you are better off either just using the GXT1000 with the NiMH battery pack (and keeping alkaline AAs for emergency use only) or getting another GMRS radio that does allow you to use NiMH AAs (e.g. a BaoFeng UV-5X or maybe the GMRS-V1).

 

[Dave_H]

I recently upgraded to AA rechargeable 2100 MAH. It takes 4 of those or can use alkaline as well. First question is when the radios go dead and I go to recharge the batteries (3 units) only one of the four batteries for each single two way radio is dead the other 3 are showing good. Because it happened on all three radios I am assuming this is normal??? Is that normal for rechargeable??? I either won the dead battery lottery or I'm confused about principle because I thought they all drained equally.

The problem with multiple rechargeable cells in series where one goes dead before the others is unfortunately common, "normal" would not be the right term. It can result in damage to the dead cell as running load current through it from the other cells is in effect reverse-charging the dead cell.

It is related to the low-voltage cutoff of the device, if any and user ability to stop using before running down too far (which is tricky). You might be able to manage it but not avoid it.

Cells in a set should initially be closely matched being the same brand, type, capacity, and age condition (not mixing new/used cells even if otherwise identical). When changing and charging, don't mix them up with other cells from other sets. Charge cells in the same charger each time (I am sometimes tempted to split cells between two different chargers, to save time).

BTW replacing a bad/weak cell with new one is not good as the new one is not matched to the others. You need to swap out the set.

Alkalines under high load are not going to give 1.5v each for very long. Their internal resistance is higher than NiCd/NiMH especially at low temp. Not sure how all this affects TX power. You could do some tests with a simple field-strength meter.


Dave


I should add that for professional two-way radio packs, cells are "graded", sorted to match capacity within the same pack. That may be done with supplied packs, maybe not, but rarely with individual cells by consumers I would think.

 

[Lynx_Arc]

It is possible these devices have some parasitic drain to them, that is even off they sip tiny amounts of current and don't shut off at voltages unsafe for nimh cells. If you have cells that aren't very closely matched one or more will hit 0v under the load if the device can operate at that low of voltage and often you can have cell reversal that is the dead cell has power going through it from other cells and that charges it in the opposite direction which can damage the battery. Because of all the Nimh cells I've had damaged operating devices using them in series I've made an effort to abandon nimh cells used in series as much as possible for lithium ion technology. Some nimh cells are more fragile and are more easily damaged in series when devices operate at unsafely low voltages for them. AAA eneloops are a lot more fragile than AA regular eneloops (2000mah) while the pros I would guess are more fragile than them.
Gone are the 3AAA and 3AA devices when I find 18650 versions. I've gone from using mostly nimh to using them mainly in single cell devices and in devices that there are no other choices.
My advice on these batteries is to find out how much power the device takes and estimate the runtime using current batteries and when you use them 50% or more recharge them without fail and when you estimate 75% usage of them at one instance try and shut them down and recharge them. I would also strongly recommend trying to see if there is any parasitic drain to them as if they are draining batteries on standby you may need to charge them on a schedule even when not using them at all to prevent battery damage or take the batteries our or a little trick I've cone is put a slip of thick paper or plastic over one end of one of the batteries to break the circuit and remove it when needing to be used.

 

[Dave_H]

If four cells seems like a problem, try six or eight series cells, which some two-way radios use. Lithium would be nice but does apply to all products. Two-way radio has mostly converted though.

I measured a couple of older GMRS radios, found standby 1uA or less which is swamped by self-discharge of the cells, therefore not a big concern. But, disconnecting cells during storage, interrupting standby battery current may or may not lose some user settings; one of the radios did after an hour or so.

Someone gave me an older Cobra GMRS radio/charger which uses a Li-ion 7.4v battery. Spares are likely not cheap and easy to find. At least some newer radios use Li-ion or Li-polymer batteries but it limits you to that brand's products and prices.

Dave

 

[turbodog]

...


I should add that for professional two-way radio packs, cells are "graded", sorted to match capacity within the same pack. That may be done with supplied packs, maybe not, but rarely with individual cells by consumers I would think.

For what it's worth... I used to have a battery grader. It could cycle individual cells at a variety of charge/discharge rates (up to 30 amps). I would get bulk cells, rate them, and assemble packs.

I never found cells that were off by more than a percent or two.

 

[snakebite]

your radio is likely designed to run alkaleaks into the dirt.
since there is a rechargeable pack no effort was made to prevent over discharge of aa since disposables are ASSumed.
what do you expect for a cheap consumer product?