After doing the same thing, only then did I realize how much money I saved at a local battery shop that was clearing out floor space. I got 4 40AH 'matched' batteries for $1/AH. They became the backbone of my power pack, and I ended up with almost double the storage for 1/3 less cost than the single 90AH battery recommended for my panel.

I need a lawn-mowing room-mate!!

I talked to my alarm company technician friend last night and it sounds like I can have as many used 12v 7Ah batteries as I can take, probably gratis. He says they replace many each week. Some are actually worn out, but others are still good (e.g. replaced when one battery in a parallel string setup croaks before the others, but they replace the whole string).

I'm meeting him at their shop this afternoon, where he says they have a milk crate full.

Then I'll just need to set up a testing rig to figure out which ones still have life in them & measure their capacity.

Woo, good news.

Testing shoudl be pretty simple, charge em up, put them on an inverter and time how long it takes to discharge them at ~1C. A 75W bulb would do nicely.

That's the plan!

12v battery > DC-AC inverter > Kill-a-watt meter (to record time & watts used until inverter disconnected) > 110v load

= good battery condition data

Cast-off Electric Mower
 

Awesome...I hope to acquire an electric mower by similar means, and replacement batteries using tips from the other posters. Then I take one more step away from the prevailing petro-culture...:cool:

Update: batteries won't be free! Sadly, my guy found out that someone already comes and buys the used batteries from his company on a regular basis. Pays 200 bucks for about 3 milk crates full (about $2 per 7 Ah 12v brick, by my estimate).

I'd happily pay that amount, but I'm not sure if my guy has the authority to sell them to me.

Still investigating!

and that guy probably takes them to the local swapmeet and resells for more

Probably something like that. There aren't any swap meets around here that I know of, but I wouldn't be surprised if it's someone from out of town making the rounds of the alarm companies.

Anyway, I got one freebie used 12v/7Ah from my friend. Haven't tested it yet. One isn't really useful to me at all.

I asked him to ask his boss if he would sell me some (I'd take a dozen for sure) at the same price he gets from the other guy.

an embarrassment of lawnmowers
 

Mower #2 ....

OK, maybe I need to start another thread...

This morning, there was another electric mower at the curb - literally at the neighbouring house to the one that chucked out the battery mower last week.

This one's a small "corded" 110v AC machine, 7A rating.

The handle is pretty bent, and has been repaired (not very well) a few times. I knocked on the door to make sure they were actually throwing it out:

"Yup!"

"Does the motor work?"

"Yup -that handle is no good. Squashed it with the car."

So I rolled it over to my place, plugged it in and cut the grass with it :). The handle definitely needs some patching/welding - it's work fatigued in several spots (not too far from breaking) and has been lightly patched up with tin & screws.

And 7A might be small enough that the inverter at the shack will be able to fire it up so I can cut the grass there with the solar power setup.

Gives me something to use while I'm sorting out the battery situation.

At 7 Amps, you'd need 1000W inverter minimum to supply the constant current, and since that supply would be continous you're going to need heavy cabling to handle it. Drawing that constant current from a smaller battery may exceed its chemistry.