Are household batteries the same as automotive?

Obviously not, automotive are much bigger, denser, and expensive. 

But automotive batteries are only made by what 3 companies? Are household batteries the same, in that regard?

I'm looking for rechargeable D cells, 4 or 8 of them actually. I've found 2 packs of energizer without a charger, and 8 packs of "Amazon basic" and random engrish brands with and without chargers, but can't seem to track down a big pack of branded batteries with a charger. 

This has me wondering if all the engrish brands maybe share a manufacturing plant with the name brands, at least in regards to the rechargeable lines.

We have stick on LED lights in our showers because that was easier than cutting out tile and running wires. The thing is, they're motion activated, so every time someone goes into the bathroom they kick on, whether they go in the shower or not. With up to 4 people sharing a bathroom, we get maybe a month out of the 4 batteries the lights hold.  Seems to me to be the perfect place for a rechargeable, but finding anything bigger than a AA from a reputable brand is difficult and expensive.

Thought.... D-cell batteries are 1.5v and 61.5mm long.  18650 Li-ion batteries are 3.6v and 65mm long.

LEDs usually have a relatively broad range of voltages in which they will work.  A common "size" is 5-12v.  Since your 4 D batteries likely install in series, you have 6v.

My idea... Cut some aluminum, copper, stainless, whatever rod into two 62mm lengths and install in two of the batter slots.  Install two 18650s in the other slots.

18650s are stupidly common.  Laptop batteries, cordless tool batteries, vape machines for addicts, some EV batteries, Tesla walls... they're everywhere.  You can usually buy them as a kit with 8 batteries, a 4-slot charger, and it comes with two flashlights.  Like this one for $22

Or you can scavenge some batteries from something you have that won't charge very well, like old cordless drill batteries.  Usually the whole pack gets ruined by one or two cells that don't want to charge.  Buy a charger that tells you how many mAh they hold so you can identify the crappy cells.

That's a really long way of saying.... 18650 batteries are a little more than double the voltage and about the same length.  Have fun experimenting.

There's only one use for "C" cell batteries...

In reply to ShawnG :

some still prefer ones that plug in the wall...

Wire them for wallwarts.

03Panther said:

In reply to ShawnG :

some still prefer ones that plug in the wall...

We've burned out two of the plug in ones. 

The Engrish names all do share a plant, yes. Typically China sorts their quality by price; I don't remember what adage it comes from, but culturally they feel like if you didn't do any due diligence to check veracity of a product it's on you. I think there's only a couple of state-ran plants.

Those rechargables are likely NiMH which has a similar voltage as alkalines, 1.65v or so I think. Outside of a brand called 'eneloop' they tend to self-discharge within a month. Curtis probably has the best idea here, it's actually pretty easy and safe to bodge something together with lithiums and LEDs because they just don't pull enough power to make them heat up.

In reply to Curtis73 (Forum Supporter) :

That sounds like a great plan actually. Awesome. Thanks for the idea. 

I had another thought on the 18650s.

The overall capacity of 18650s is lower than D-cells.  To prevent more frequent charging, (and if you're into some fun hacking), you could skip the dummy cells and run four 18650s in series/parallel.

Your lights with D-cells are likely wired like this to get 6v:

What I suggested is to do this, which is 7.2v, but they won't last quite as long because 18650s have a lower overall capacity:

So maybe four 18650s and change the terminals in the lights to look like this?

Depending on how the battery boxes in the lights are assembled, it could be super easy, or it might mean soldering irons and other craziness.  Worth a look.

In reply to GIRTHQUAKE :

In the western world, at least, that's "buyer beware", or "caveat emptor"