possible plot hole regarding batteries

I don't know for sure, but it seems to me people lacking modern production facilities would not be able to make their own dry cells as we know them. Rechargable batteries probably wouldn't hold up for 20 years (mine start to go kaput about about 5).

That doesn't mean they couldn't do some sort of science-fair type improvisations. There are probably plenty of solar panels lying around, and although these too don't last forever that might be a plausible way for your characters to get their power. There are also crank-powered dynamos (didn't the WWII field phones work on this principal?).

Another option is to have some improved source of batteries widely available prior to the collapse of your previous society. It might come off cheesy to develop a whole new technology just as a band-aid to solve a later story problem, so less might be more in this respect.

Have you looked into food batteries? I have no idea if they would be practical or powerful enough for what you have in mind, but they might be an alternative to using off the shelf batteries or manufacturing batteries.

http://www.madsci.org/experiments/archive/889917606.Ch.html

What about rechargeables? I think if they're in a discharged state, they'll basically last forever.

Building simple batteries is easy enough, even for a low-tech society. The problem is those batteries will be orders of magnitude larger than the ones they replace. If someone has a radio with a large (probably the size of the radio) tin box fastened to the back to house the batteries in a post-apocalyptic setting, I wouldn't blink. Give the batteries a shorter lifespan as well and I'd totally buy it.

I'm talking about dry cells. They're really not that tough to make, I'd have to look it up, but I think all you need is a sheet of two different metals (I don't know which work best) and paper towel/coffee filter like stuff in between. Fill the layer between with an acid solution and off you go. Dry cells aren't really "dry" they're just soaked into a medium between the metal plates, rather than liquid sloshing around.

Kids' chemistry-set experiments commonly feature making a battery out of strips of zinc and copper stuck into something like a sliced citrus fruit. Batteries don't need to be very high-tech.

caw

You just need something in the water that has protons in it - so various dilutions of sulphuric acid in car batteries, the citric acid in a lemon etc... Some work better than others but its what you can get. You need an modern industrial base to have sulphuric acid readily available. (You can make it in a chemi-set, but how many steps do you want your characters to go through.) Mind you, sulphuric acid would last years, so you can find a chemi store.
Also note - stronger acids like sulphuric will dissolve some metals (you'd have to check which ones) which is why lead is used in lead acid batteries.
But
There will also be erosion of electrodes by electrolysis. I've forgotten the details but its pretty basic chemistry.
With lead acid batteries, what ends their life is some sort of crud building up on the lead plate - the crud being an insoluble lead compound, which doesn't go away when you charge the battery.

Different designs of batteries respond differently to charging cycles and some live longest if not fully discharged every time.

Or stick with lemons and chuck away when mouldy.

Ah - one other thought. Voltage and amps. Devices will have a tight range of requirements for voltage and amps. Different batteries, different outputs on those. You might want to have a bit of trouble for your characters in refining that aspect. No idea what amps and volts you get from the lemon....

Mr.Letterman said:

Also Drachen Jager, you said tin for the housing. I'm only just learning about this now but would it have be a non-conductive housing. Say pottery, glass, plastic? If tin is ok that would be great.

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I meant to house the battery, not as the battery. You'd need to attach some extra-large compartment to the radio, IMO that would be easiest with snipping up some tin cans, maybe a few rivets, now you have a box attached to the radio that's big enough for your low-tech batteries. The battery itself still needs to be enclosed. If you're doing post-apocalyptic tech, they'd probably recycle, perhaps jam jars or plastic drink bottles as the outer layer of the battery.

Note also, the difference between cells and batteries. If you don't know it, you should look it up. If the person who makes the batteries/cells for your survivors ever appears in the story they should know the difference, even if other characters get it wrong.

As an aside, I don't think anyone's ever called cray a plot hole before...

Angry Guy said:

As an aside, I don't think anyone's ever called cray a plot hole before...

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I assume it was a typo.