They have some demos on their website

https://phyphox.org/experiments/

This is only applicable if you drain them all the way repeatedly (over draining of the battery leads to sulfate forming on the plates which is)

https://www.sciencedirect.com/science/article/abs/pii/S0378775303009340

I combat this by over sizing my batteries. I have a lead one in a tool box I use for camping and I recharge with a solar panel, It’s a standard car battery that for my use lasts 6 hours or so. Normally I use it for a couple hours (between dusk and time to go to bed) to use a laptop, maybe a speaker and an LED light and then I charge it during the day while I go hiking via solar panels.

If you care for them they can last a long time. There’s also charge controllers you can install to keep it between 20 and 80% charge (for best life) but that’s kind of overkill for my purposes.

Having said that, yes … deep cycle batteries are a lot better, and even more so are Li Ion and solid state … but they are also significantly more expensive, and I like to use whatever I have at hand.

This one is a very small 3Ah battery because my friend is using it as a proof of concept. He wants it to power a very small Wi-Fi spectrum analyzer / packet capture device when he goes war driving.

The beauty of Lead acid batteries is that they’re very cheap at the cost of additional weight and volume If I used 18650 Lithium Ion cells I could probably get more than twice the battery capacity, but it gets more expensive and more complex (You have to do some math to figure out how to wire the batteries to add up to 12V and calculate how many amps total so you can fuse it correctly)

In the pic you can see that there’s already a float charger I’ve taken out of the case to reduce the volume it takes (I normally encase them in epoxy) and an Inverter I’m going to wire externally for him to test 110 with a battery this small

I still have to cut holes for the USB adapters and float charger port, and I have to shop for a volt meter monitor that fits his needs.

If price is your main concern make one yourself. Specially if you don’t need 110

1. buy a 12v battery of your choice (deep cycle are best, but car batteries will do in a pinch, UPS batteries if you want small)

2. buy a tool box of adequate size for your battery, allow for extra room

3. order a “float charger”

4. Order USB and cigarette lighter ports as desired

5. wire it all up inside the toolbox

I’ve made a few with minimal effort, they’re great for camping and my latest one even allows me to jump start a car

There are plenty of guides out there with more detailed steps

https://www.youtube.com/watch?v=49Do__99Yr4

I’m currently making one for a friend, let me know if you guys want to see pics of the components