Questions tagged [batteries]

An electric battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy

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311
votes
6answers
66k views

Why is there so much fear surrounding LiPo batteries?

I've been trying to design a charging system for a small robot powered by a 2S 20C lithium polymer (LiPo) battery. Were I to trust everything I read online, I would believe that the LiPo will kill me ...
89
votes
5answers
240k views

Why are there 3 pins on some batteries?

Lots of new batteries (for mobile devices, MP3 players, etc) have connectors with 3 pins. I would like to know what is the purpose of this and how should I use these three pins? They are usually ...
78
votes
10answers
30k views

Batteries. Why use 9V?

With all the technology available today with being able to boost voltage efficiently using SMPS, why do we still use 9V batteries? Is there some secret advantage with them that I am unaware of? If ...
66
votes
12answers
8k views

I am a quadriplegic. Would it be possible to power my ventilator humidifier with a battery?

I am an absolute novice in regards to electrical engineering, and so I am hopeful your expertise can guide me in the right direction. I know this is an unusual post for this forum, and so I thank you ...
62
votes
4answers
309k views

Does mAh measure how long a battery would last?

I know mAh tells how much milliamperes a battery can deliver in an hour. But does that also tell how many hours the battery would last? Sorry but I don't really get it. If we're talking about a water ...
55
votes
3answers
10k views

Lightning bolt vs. batteries: a coulomb in everyday terms

I am trying to decide if the information on the wikipedia page http://en.wikipedia.org/wiki/Coulomb#In_everyday_terms is reasonable. In particular the statements that a lightning bolt has about 15 ...
53
votes
7answers
109k views

How should I use a multimeter to determine which AA batteries to keep and which to toss?

I have a bag of about 50 non-rechargeable AA batteries (1.5 V) that I have collected over the years. I bought a multimeter recently and would like to know the best way to test these batteries to ...
45
votes
3answers
37k views

When a battery is your power source, what is ground?

For the sake of not incorrectly connecting my power supply and damaging my board I'm going to ask a relatively dumb question. Is ground on my board the negative terminal on my battery? Explicitly ...
42
votes
8answers
16k views

Why are car batteries still so heavy?

Back when I was a kid, car batteries used to be huge heavy lumps of plastic filled with lead and acid. They used to weigh almost as much as a mobile phone (slight exaggeration there, sorry). 45 years ...
42
votes
8answers
77k views

Can a 12V battery give you a shock or not?

I am reading a book called "Make: Electronics" and, on page 9, it says: "Anyone who has dropped an adjustable wrench across the bare terminals of a car battery will tell you that short circuits can ...
39
votes
7answers
15k views

What is the truth about 1.5 V “lithium” cells?

At least one manufacturer out there is marketing "Lithium" cells in familiar AA and AAA sizes, as direct replacements for those standard 1.5 V sizes, boasting the typically better than alkaline ...
38
votes
3answers
29k views

How is wristwatch with 10 years battery life possible?

Turns out Casio offers a handful of wristwatches with "10 year battery life". The claim is that thanks to "an advanced technology" the battery life in those watches is extended to ten years. Now if ...
37
votes
5answers
10k views

Are decoupling capacitors needed with battery power?

Currently I run all my gadgets from batteries and don't use decoupling capacitors. Are they generally needed/useful when drawing energy from a battery?
36
votes
4answers
84k views

At what voltage is a NiMH battery empty?

I have a battery pack of NiMH batteries. It is ten cells with 1.2V, 4000mAh each, put together in series. So rated voltage is 12V. After charging, i.e. when the charging device says that it is ...
35
votes
3answers
172k views

Why do we connect a battery to ground when jumping a car?

This may seem like a very simple question, but I've searched all over the place and haven't found an answer. When jumping a car, we connect the + end of the charged battery to the + end of the dead ...
34
votes
1answer
8k views

If I am measuring 2.3 V on a 1.5 V AA battery from Duracell, is my multimeter broken?

I recently measured a brand new Duracell AA battery which is labeled as 1.5 V. The reading was 2.3 V. Is this ever normal for a fully charged battery, or is my multimeter broken?
34
votes
5answers
55k views

Regulated 3.3V from a Lithium-ion (or LiPo) battery

Background I wish to power my circuit with a Lithium-ion or LiPo battery (likely a battery with around 1000 mAh capacity). These batteries have a voltage that goes from 4.2V to 2.7V typically during ...
31
votes
2answers
12k views

How to calculate battery life

How do I calculate how long a battery operated product will run? Here's what I've got: 2 AA, 1.5V, 2700mAH batteries Voltage Regulator with a Iq of 25 uA Voltage Regulator Eff = 80% Active Current = ...
30
votes
8answers
42k views

Current flow in batteries?

I am reading a basic electronics book: "There are no Electrons: Electronics for Earthlings" and I came across a clever passage about the fact that you need a closed circuit in order for current to ...
30
votes
3answers
10k views

Negative voltage on AA battery

Last night I pulled the battery holder out of a toy RC car to test the voltage with my meter. The pack has 4 AA batteries. The combined voltage at the terminals of the pack was well under 1 volt, ...
28
votes
3answers
16k views

Are coin cells a suitable replacement for AA batteries?

I am currently using AA batteries in my projects but would like to look at cell batteries for my next project, due to their compactness. Apart from the physical appearance, how do cell batteries ...
28
votes
4answers
138k views

How to measure capacity of a Lithium-ion battery

I bought a Lithium-ion battery for a camera (much cheaper than the brand replacement but non unreasonably cheap compared to AAA Li-Ion batteries with similar charge). I however have doubts that it has ...
27
votes
7answers
26k views

Least expensive way to boost DC voltage

What would be the least expensive way to boost a DC voltage? The aim is to convert 1.2 V/1.5 V (from an AA/AAA cell) to 3.3 V to power a small 8-bit microprocessor, like Atmel ...
27
votes
5answers
4k views

Charging lead-acid batteries?

Are there any special requirements for charging lead-acid batteries?
26
votes
5answers
5k views

Making a battery last a long time in a microcontroller circuit

I'm hoping to power an ATtiny85V for a nice long time on some small battery, probably a coin cell. I've looked into the software side, and my code is watchdog timer driven, has unused analog and ...
26
votes
3answers
4k views

Why do batteries recover after a load is removed?

I carry a small 2-AA flashlight, and a few times, I have accidentally left it on in my holder. Each time it dies completely, so that no light is emitted, but if I turn it back off and wait for a few ...
25
votes
3answers
14k views

Does leaving a cell phone on charge all the time weaken the battery, and why?

If I leave my cell phone with the charger plugged in all the time, would this weaken the batter, and why? I've heard that you should only charge the cell phone when you receive a 'battery low' message ...
24
votes
5answers
4k views

Why are off grid solar setups only 12, 24, 48 VDC?

I am looking to produce 50kW for an off grid solar project. Ideally, I'd like to have a high voltage DC battery system with a high power battery inverter and charge controller. I have only found a ...
24
votes
5answers
9k views

How could have Banksy kept an RF receiver running for 12 years? [closed]

I'm talking about Banksy's "Girl with balloon" painting that shredded itself at auction. I think the general consensus is that he didn't, and that it was set up before the auction (or a couple years ...
24
votes
6answers
281k views

How to Calculate the time of Charging and Discharging of battery?

How do I calculate the approximated time for the Charging and Discharging of the battery? Is there any equation available for the purpose? If yes, then please provide me.
24
votes
3answers
33k views

Why are deep cycle batteries rated in amp hours instead of watts hours?

Why are deep cycle batteries rated in amp-hours instead of watt-hours? For example if I see a 85Ah battery, I multiply 85Ah x 12V to get 1020 watts. As household electricity use is measured in watt ...
23
votes
3answers
143k views

How to compare mAh and Wh

When looking at consumer electronic devices with batteries I sometimes see the battery capacity listed in Wh (watt hours) and sometimes in mAh (milliamp hours). I would like to be able to compare the ...
22
votes
14answers
4k views

What can I put a kilowatt into? (Or: help me save my hairdryers)

TL;DR: I need something to discharge roughly 160A at 14V into, or 2.24 kilowatts. Any comments, or answers, with either a) something I can dump a kilowatt into, b) some way I can modify a common item ...
22
votes
5answers
26k views

Whats does “hr” mean among “V” and “Ah” in batteries?

I have a battery which indicates 12V25Ah/10hr. What does 10hr mean here? I guess "hr" stands for "hour". But 25Ah already means if battery is fully charged and if I load 12V 25A (=300W) to it, it ...
22
votes
3answers
862 views

Identify this rechargeable battery pack

I want to identify a rechargeable battery pack from inside an old portable hard-drive. It is unlabelled. (I ripped open the blue covering - it isn't labelled on the internal metal cover either.) ...
20
votes
6answers
7k views

Can I disable a battery powered device by reversing half of its batteries?

When I have a device that is powered by two batteries, can I disable it by turning one battery around? For illustration, the purpose is to leave batteries in the device for storage, but it does not ...
20
votes
7answers
4k views

Why do batteries in consumer electronics get used unevenly?

When changing the batteries of kids toys, remote controls, etc., I test the batteries and have noticed that they drain differently. One will be dead and the other is still in the green. Why does this ...
20
votes
6answers
35k views

Why are batteries measured in ampere-hours but electricity usage measured in kilowatt-hours?

I was reading about energy usage in batteries and don't quite understand why it is measured in different units than home electrical usage. An ampere-hour does not include a measure of volts. But my ...
20
votes
3answers
30k views

Batteries in series with different amp-hour ratings.

I have a 1.5 amp-hour, 12 V battery and I have a 10 amp-hour 12 V battery. I know the voltage will increase to 24 V when they are put in series, but I don't know what goes on amp-hour wise. Does the ...
19
votes
5answers
4k views

Why is the battery jumpered to a resistor in this schematic?

I am looking at a schematic for the wifi D1 mini data logger shield that I'm using right now. In this part of the schematic, a coin cell battery powers the RTC. I see R5 is jumpered across the ...
19
votes
3answers
9k views

How can I design a circuit that will turn on when a wire is cut?

I'm trying to build my own cable lock alarm (for science!) and am having trouble figuring out a way to detect that a wire has been cut. The circuit has to Use no power at idle (or at least, very ...
19
votes
4answers
2k views

Supercap compared to a battery

What is the current state of things when it comes to super capacitors and batteries? Are super caps anywhere near rivalling LiPo's in capacity? I've often heard people talking about super caps as ...
19
votes
2answers
62k views

Adding mAh when wiring battery cells in series?

When combining battery cells in series, the voltages of the cells are added to get the voltage of the final circuit. Do the mAh add up, or stay the same? For example, suppose you have two 3.7V cells,...
19
votes
4answers
1k views

How can embedded systems estimate their battery status so precisely?

As I understand it, the terminal voltage of batteries changes a little on charge/discharge, but these changes are minimal compared to other effects (temperature, minor manufacturing differences, ...
18
votes
9answers
8k views

Is it safe for a CR2032 coin cell to be in an oven?

I'm designing a portable temperature logger that I would like to be able to measure temperature within my home oven. I plan on designing a mechanical enclosure to hopefully protect the design from '...
18
votes
5answers
3k views

Does a capacitor connected directly to a battery consume any energy?

In this example simulate this circuit – Schematic created using CircuitLab After the initial charging of the cap to 3V, current gets blocked, but over time does it consume any energy from the ...
18
votes
2answers
2k views

Help identify the discrete component in this battery pack

I am rebuilding a NiMH battery pack for a RF remote control device which can be recharged by plugging the device in. The battery pack is connected with three wires: black to the negative red to the ...
18
votes
5answers
4k views

Why are lithium ion cells mostly round?

After watching some tear-down videos on YouTube with various lithium battery products (portable chargers, laptop battery, power tools) they all (apart from mobile phones / tablet battery) seem to ...
18
votes
4answers
39k views

Why is it bad to mix new and old batteries?

I've seen warnings that it's bad to mix new and old batteries -- why? Is it a matter of a battery's age or a battery's voltage/current (remaining)?
17
votes
5answers
14k views

How to solder wires on Li-ion cell phone batteries?

I am making a obstacle avoiding robot and wanted to power it with mobile phone batteries. But wondering how to solder wires on battery correctly for no inconvenience. p.s. I am a new arduino ...