lLi-Ion battery charging question

On a sunny day (Thu, 1 Jun 2017 15:47:55 -0700) it happened "billbowden" wrote in :

If one is empty and one full, then you may get a very high charge current from one battery to the other, but I do not know what the internal resistance of those batteries is, nor their maximum charge current. Without that data maybe better discharge both first, or charge one at the time.

It's also useful to check the voltage after termination. I bought two batteries from ebay. They measured zero volts when I got them, the overdischarge protection had kicked in. They wouldn't charge past about 8V. Turns out that the cells were imbalanced. Took it apart and charged each cell to 4V to equalize them. Problem solved.

My multimeter quits at about 7.2V. I was worried about life, but it's still working fine. Other stuff, not so much.

My guess is that you got a NiMH battery (7x1.2) and not LiIon. This would also explain that you got the simple charger you describe. Charging LiIon is challenging and can produce nice fireworks. You would definitely not want to charge them in parallel.

Pere

NiCd must be pretty ancient, but "9V" batteries can be had in 3 versions nowadays: 7.4 V, 8.4 V and 9.6 V nominal.

At the time I looked, I found no affordable low self-discharge

Low self-discharge and Ni don't go in the same sentence. The only commonly available secondary batteries with low self-discharge are Li*.

Yeah, sorta. LiIon 9V batteries come in 8.4v and 9.6v versions. NiMH also come in 8.4v and 9.6v versions:

Tenergy, Ansmann, EBL, and Maha/Powertex make LSD NiMH 9V batteries. Notice the difference in rated voltages. Prices run $5 and up: LiIon 9V batteries are cheaper and have twice the capacity:

For the Tenergy 9V LSD NiMH cell: It uses 7 cells for a total of 8.4V. I have some in various pieced of test equipment (LRC meter, DVM, ESR meter, function generator, watt meter, etc). No problems with self-discharge for about the last 12-18 months. I haven't bothered to measure the low voltage cutoff for my various instruments.

Like most or perhaps all NiMH batteries, I've found that I have to charge and discharge the battery at least once before it deliver full capacity. These graphs is for "ordinary" NiMH AA cells. Notice the increase in capacity with each discharge cycle: I assume (famous last assumptions) that a 9V LSD NiMH battery acts in a similar manner.

I beg to differ. LSD (low self discharge) NiMH are quite common and quite good: I've been using various generations of Eneloop batteries for several years. I check my batteries about once every 6 months. They typically have 90 to 95% of full charge (based on terminal voltage) with nothing connected. See charge retention tables at:

On a sunny day (Wed, 07 Jun 2017 23:01:18 +0200) it happened Dimitrij Klingbeil wrote in :

Are there any of those lipo based 9 V batteries that have a single 3.7 V lipo and a switcher to 9 V exactly inside? If not why not? I have a 3.7 V to 5 V switcher that easily fits in a 9 V battery in a project to power a GPS module, been in use for years.

I had a device that worked like that years ago. Think it might have been an HP calculator.

Problem with a general purpose device like a battery is that it has to be able to deliver a lot of current, but still be extremely efficient at very low currents... like zero current load.

Also, battery operated devices are designed to operate over a wider range of input voltages. Regulation might be an extravagance.

Tell us more about the efficiency profile for your device.

None that I could find. That's basically the idea behind all those cell phone charger battery packs that are commonly available. A 9V version should be easy to do.

While you're at it, an internal battery charger might be useful: Maybe throw in an LED flashlight for good measure.

Cost, reduction in capacity, and lack of benefits. The added electronics would probably raise the price. The reduction in available volume would decrease the cell capacity. When done, you would end up with an expensive reduced capacity 9V battery, that doesn't do anything more or better than the current practice of cramming 2 LiPo or 3 LiIon cells into the same package. There's also the possibility of generating EMI/RFI from the inverter.

Rhetorical question: What feature of a single cell plus boost inverter 9V battery would you advertise that would make someone buy it at a higher price than just a battery package? Short circuit protection perhaps?

On a sunny day (Thu, 08 Jun 2017 09:14:44 -0700) it happened Jeff Liebermann wrote in :

Exactly, that is the idea, I use a MCP73831 charged from USB or solar, for my GPS based clock, radiation counter, data logger.

Well, the OLED display is always on minimum brightness, it is blinding if set to maximum.

Just for fun, I modified one of those mechanical rotary cellphone chargers from ebay and put in a high effciency white LED. Who needs batteries, just keep turning the handle :-)

I use that charger chip in several projects bluetooth receiver for example.

Yes EMF could be a problem but the 9V batteries I have seen looked like a metal case.

Indeed short circuit protection, and CHARGE protection. Those MCP73831 are really very good, this 1 Ah lipo I use has ben charged and discharged now a thousand times, its capacity is a bit less now, but I put it on USB in the morning and it shows a clock at night. Note there is no limit on the solar cell output to the lipo, mainly because the sun is so weak here... Else just connect the solar cell to the charger chip...

Note that many of those lipo batteries already have a chip for protection inside, one more chip, and inductor, capacitors... 1 resistor.

In very large quantities it should not be that expensive.

Yes, never used those, I bought 4 cheap digital multimeters on ebay:

On a sunny day (Thu, 08 Jun 2017 07:30:13 -0700) it happened mike wrote in :

Dunno, would have design one and to measure it...