OK I am weird, as a 3 year old (1954) I'd swipe my father's WWII MX-991/U flashlight. This is the standard right angle headed unit. I'd hide in closets, under the sink, under beds, in the small room the water heater sat in (under the stairs) and enjoy the light in the dark.

Dad was frustrated, "D" cells weren't horribly expensive, but he grew tired of having to keep a supply. Mom took the view point "At least he's not using candles."

A friend of Dad's worked for GE and gifted our family with early NiCad cells and a charger. Dad bought me my very own MX-991/U and I'd sit in the closet and listen to my "Boys Rocket Crystal Radio."

My maternal grandfather gave me a very old Prango 2 "D" cell flashlight with a patent date of Sept 28, 1915.

This unit uses a small silver plated "parabolic" reflector with a large glass lens.

Thus began my collection of flashlights.....a collection continues to grow, I've never met a flashlight I didn't like.

All of this is of historic interest and perhaps offers a view into my somewhat odd psyche, but what on earth does it have to do with Electronics 101.

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I could go into the vibrator powered electroluminescent light my dad built for me, or how my uncle replaced the vibrator with a pair of germanium power transistors, or how I made my first LED flashlight, it used red and green LEDs and either or both could be enabled, but I won't.

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[And for you with dirty minds....

https://en.wikipedia.org/wiki/Vibrator_(electronic)]

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Your portable electronic gear operates from batteries, unless you have a hand held generator or can operate off PV cells in direct sunlight.

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A friend gave me an interesting book. This book is almost mandatory for those of us who operate equipment from batteries

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Batteries in a Portable World: A Handbook on Rechargeable Batteries for Non-Engineers, Fourth Edition?

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It is available at Amazon (and at the ARRL), it is a bit expensive at about $30.

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I still distrust secondary (rechargeable) lithium batteries, but they are a factor of modern life and, unless I wish to give up my cellphone, laptop PC, portable equipment, I have no choice but to learn to live with the !@#% things.

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The book starts out with the basics of batteries and might appear too basic for a serious hobbyist, but it gets down to brass tacks with reasonably detailed information on many different types of batteries, their strengths and weaknesses. And all batteries have both.

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[And for you with dirty minds....

https://en.wikipedia.org/wiki/Vibrator_(electronic)]

Batteries in a Portable World: A Handbook on Rechargeable Batteries for Non-Engineers, Fourth Edition?

As Donald pointed out, alkaline cells/batteries have a fairly high internal resistance, the old carbon zinc Leclanché? cells had an even higher internal resistance.

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[I had to go pick up a prescription and checked out the battery rack and found old style carbon zinc Leclanché? cells are still available, I'm not sure why anyone would try and save the few pennies difference in price, but then some people are even cheaper than me.]

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It's much like using CR3032, or other lithium button cells, to power a LED. It's almost always perfectly safe to overvoltge the LED because of the high internal resistance of the button cell drops the voltage to a safe value.

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My wife won a 6 cell Mag flashlight with a "psychedelic" color scheme in the anodized aluminum case. She loves the thing but hated the way it ate batteries. [God help the person who tries to attack her when she's got it out. I suspect it'd make one heck of a club.]

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I replaced the incandescent bulb with a LED and new reflector then used "AA" to "D" adaptor shells. It's about 3 times as bright and the cells last about 5? times as long.

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Note: Drop in LED replacement bulbs for incandescent bulbs for "Mag flashlights" are inexpensive but the original reflector isn't optimized for a LED. It's worthwhile the extra expense to go with a combined LED/reflector. [or buy a new LED flashlight for about 1/10 the cost.]

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The book goes into such things as internal resistance, response to cold and heat, etc.

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I use 1F [yes 1 Farad] capacitors to replace the CRxxxx memory backup cells in my Kenwood R-2000s and iCom IC-28A. I salvaged the 1Fs from Kenwood "keep alive while shipping" commercial 2-way 900MHz radios. They've been in service since the summer of 1990. I just turned on a R-2000 that has a really messed up encoder reader. You can tune the radio but it will take an hour to tune to a desired frequency. It's tuned to WWV on 2.5/5/10/15/20 and the US AF global HF network primary and secondary frequencies. It hadn't be turned on, or connected to power, in at least 3 years. All memories were still there.

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For the truly demented among you, with oodles of money to waste on experiments....

Electronic Goldmine offered

G28718 ^' Eaton 62 Farad 18.0V 3.7KW Peak Power Energy Storage Module XTM-18R626-R

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Eaton Supercapacitor Storage Module is rated 62 Farad 18.0V. Size is 9-1/4" x 1-5/8" x 3" tall. Has 2 screw terminals for power hookup. New! Retails for $189.69.

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From the Eaton webpage

https://www.eaton.com/za/en-gb/skuPage.XTM-18R0626-R.html

Peak Current (1 second) 235.6A

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My Toyota Echo draws 97A @60F when starting. Takes about 4 seconds, so, could I use 4 or 5 of these? At ~$600?

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These would make a nice very short term 12V power rail back up for short power outages.

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One of the "magic" ways electric vehicles maximize battery life and driving range is to use the drive motors as generators when braking, they dump the electricity into high value capacitors, then draw the electricity to start/accelerate.

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I am not into NASCAR but was at a friend's home one evening and his daughter loves NASCAR. I was impressed by how quickly the front brake would turn red nearly white from heat with what appeared to be modest braking.

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Braking clearly wastes a lot of energy, capturing it for reuse in an EV is impressive.

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Re vibrators. I tore a dead one apart when I was 7, still remember the odd smell from the sound deadening rubber insulation.

I used a relay as a 'vibrator' for my first home made Geiger counter when I was 8. The vibrator drove the 6V CT with a lantern battery (this was when lantern batteries used "F" cells instead of "D" cells.) of a salvaged transformer. A 3 stage voltage multiplier produced 600-700V. It would charge a capacitor that gave 10 minutes of "click time" before needing to recharge. I was 10 when I replaced the relay with transistors.

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I eventually learned enough to build a real voltage multiplier, use a cross coupled pair of transistors to drive a 12V CT > 120V transformer and step the ~120ish volt to 620. I used Neon bulbs to inhibit the oscillator when the voltage was 620ish.

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I thought I was a genius.?

Hey it was a lot cheaper then a 600V battery!

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I'd have to dig through my "lab notebooks." All in 3 photocopy boxes filled with notebooks and sheets of paper. I'm recovering from bronchitis, my wife would have called 911 last Friday night if she hadn't had her knee replaced on January 31 and isn't quite up to managing alone, so don't want to breath the dust.

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So, going from a 60 year old memory, something like shown

https://www.scribd.com/document/132869868/12V-to-120V-Inverter

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Note: This is not the way to do it today. Use CMOS chips to drive MOSFETs, lower loss from collector to emitter.

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Tripplite used a similar design with heavy duty germanium power transistors in their 150W 12>120V inverter.

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My unit almost certainly didn't produce anything near 60Hz, but it worked. I'm amazed at how well a lot of my projects worked when I was somewhere beyond clueless. Of course a fair percentage were total failures. I tried to build a FM wireless mic....with a germanium transistor when I was 9. I didn't have a clue about Ft.

Now the FM wireless mic with a pair of tunnel diodes did work, range about 500 feet. Yep, certainly violated Part 15 of the FCC rules.

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And my Tesla Coil got me in trouble when it sat the wallpaper on fire.... My mother disassembled that unit with a frightening amount of anger....

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To Bertho

120F.....two of them. Bet that got a bit expensive. How do they handle temperature extremes? The spec sheets I've seen mentioned serious problems below 32F. [of course that was 20 years ago.]

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General comment, don't do this unless you know what and why you are doing it.

I needed 90V one night RFN to check a surplus 6M military radio.

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I was in Eastern Kentucky between Jackson and Hazard.

Sort of limited on options....but the grocery store (IGA) had 9V batteries.

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I used 10 9V batteries, snapped the positive from one to the negative of the next. Ugly as sin, delicate as a ...er flower, but it worked.

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I've been told I think out side the box.

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There are boxes we are supposed to think in?