I am trying to help my nephew with a science project. We have built a scale model of a small town. With a water tower to supply water to all 32 homes, 8 apartment building 10 apartments each. 6 business buildings a some small stores all wired for electric and water. I told the kid no bigger. You are already going to win the 8th grade competition, guaranteed This thing really started small and just blew up. It now measures 40'x 40' in sections of 8X4 5/8" plywood. It has a train yard, 2 factories, junk yard, street lights, railroad crossing. Finally what I am most proud of is a river with a dam to provide power. Yes it does work but not enough power is produced to run the whole thing. Basically the dam runs all the LEDS and there are hundreds. The river current runs off sprinkler valves, that are timed to open every 3 secs, releasing compressed air from a PVC chamber at a low PSI. The dam itself would take me for ever to explain, but I researched dam after dam, spec it out and built it from scratch. I have always been quit the handy, crafty guy, but this has really stretched my limits.

FINALLY To my question and after all that you are probably going to laugh. I just do not know very much about batteries. Ok I need a power source to run the rest of this model. I was thinking car battery but I do not need that much current.

I have a board I built for the model, that has 44 switches of all kinds. Push button momentary, Toggle, Rocker, dimmers, some illuminated and others not. Plus I have 15 small motors running draw bridges, Train round house, some, sprinkler valves, and gates. My goal was to get everything to run off the dam, but I can't get water pressure stable enough without cause potential damage, so I must keep pressure low and get what power I can.

So the question. I have bridged 2 9v battery packs everywhere to run things. All in all I have 12 2 9v packs throughout the switch board, yep 24 9v batteries, and these thing are costing a fortune and last not long enough. I know 9v have a low Capacity 300ma or so. I just thought they would last longer than a week or so. I have been researching lead sealed batteries, from 12v 5a to 12v 33a to ATV,and Car batteries. Car batteries I am sure have way more current than I need.

Here it is the QUESTION
What size lead battery would not only replace the 12 9v 2packs, but also give me more usage????

I understand capacity, but I don't need a battery so big it could melt the rings on your hands. Besides kids will be around this.

Any suggestions???

 

SLA (Sealed Lead Acid). Nominally 6V or 12V at several Amp-Hours. Look like this.

Must you have 9V for your loads, or will 12V work directly?

 

One way is to measure the current and substitute a suitable power supply. The DC electronics area will help you with the measurements if you're not sure how to do them. This will require a meter and a little electrical knowledge.

I agree with MikeML's suggestion about using a lead-acid battery -- it's probably your cheapest approach, assuming you have a battery charger. If you don't, then you may be able to find a wall wart for $15-$20 that will supply enough current.

Without the current measurement, we can't make a specific recommendation -- you're basically asking "I want to lift this load with a rope. What size rope should I buy?" and you haven't told us the weight of the load.