Introduction: Uses for Dead Car Batteries and Sealed Lead Acid Batteries

About: Hello

Many “dead” car batteries are actually perfectly good batteries. They just can no longer provide the hundreds of amps needed to start a car. Many “dead” sealed lead acid batteries are actually un-dead batteries that can no longer reliably provide a couple of hundred watts of power needed to keep a computer running in a power outage.

A couple of years ago I decided to add another small solar panel to the collection I have on my roof. I have a 5 and 10 watt. This new one is a 20 watt. It is dedicated to providing emergency power for lighting, a small fan and other misc. small low voltage devices. For this setup I needed a battery since it would need to be able to provide power 24 hours a day. I decided an un-dead car battery would be perfect since the largest load it would need to power for any extended period of time would be less than one half an amp. There is quite a difference between 200 – 600 amps and a half an amp.

The battery pictured was one I replaced when It would no longer start my car.

Step 1: Charging the Battery

I could have used a linear regulator to charge the battery with the solar panel.  The cost of a linear regulator is typically less than a dollar.  I decided to go with a charge controller instead because they more efficiently use the available power to charge the battery.  You get more run time at night when you use a charge controller. 

There are cheaper charge controllers but after reading about several of them I went with this one.  The 20 watt solar panel is currently (9-24-12) $52.99 plus shipping at

Step 2: The Test Fan

I did some extensive testing to make sure I knew how well the system would work in an extended power outage.  I ran the fan for several weeks, 24 hours a day a couple of summers ago.  The system worked fine.  Since then I have been running LED lighting out on the patio 24 hours a day for about 2 years.

The fan pictured is a 10” 12 volt, 5 watt, 2 speed fan that was on clearance at Walmart.  They still sell them but it was the end of the season.  I have 3 or 4 of them.

The LED board has 16 leds.  The battery is not even hardly trying to power this tiny 1 watt load.

Step 3: Sealed Lead Acid Battery Powered Lamp

Here is a nice little battery operated 12 volt clip on light I made from a 120 volt light.  The 12 volt led board has four 20 milliamp type LEDS in series with a 33 ohm resistor.  So this lamp draws 20 milliamps at 12.5 volts (1/4 watt).  On the back of the board is an RCA plug that plugs into an RCA jack inside the lamp.  If I want to go brighter or use different LEDS I can unplug this board and plug in a different board.

Step 4: Lamp and Charger

I also made a desk lamp with a completely enclosed battery.

I decided to go green with these lamps and other low voltage devices I have made, so several years ago I bought a 5 watt solar panel. We do not use our chimney because we have birds (they are sensitive to smoke) so I put the solar panel up on the top of the chimney. Since the current is so low I used cat 5 cable to run from the panel to the garage. Since I only need to charge one of my other un-dead car batteries for about 4 or 5 hours about twice a month (as needed) I made a battery charging board with a linear regulator. It is a 15 volt regulator. The battery never gets up to 15 volts. I charge the battery when it gets down around 12 volts and I charge it back up to around 12.5 volts. I check both lamps every couple of weeks. They have a really long run time. A 7 amp hour battery is kind of overkill for a 20 milliamp load. It’s great. Both lights get used daily. One of them gets charged about every 6 weeks or so. Keeping the batteries above 11.5 volts makes them last longer.

The charging board also has a 12 volt regulator so I can run 12 volt devices off of the solar panel directly.

So there you have it. You can run whatever you want off of one of these un-dead car batteries. If you buy a 12 volt to 120 volt inverter you can power many 120 volt devices. Also you can run any device that has one of those plugs that pug into the car cigarette lighter jacks. You can be ready for some quick and easy camping at home in a power outage with the 5 watt set up for under $50.00 or take it up a notch with a 20 watt set up for a little over $100.00.

If you want to go really simple and cheap, may I suggest this for really simple emergency LED lighting:



Technical information on the Sunguard charge controller:


LEDS for Beginners:

It is a good idea to check your results after you make your circuit to be sure that you do not exceed 20 milliamps in the circuit. You do this by measuring the voltage across the current limiting resistor by the resistor value (ohms).


Data sheet for linear regulators:

Lots of companies make these.

Here is a link for a 12 volt linear regulator:

Cost: about 18 cents. You may need a heat sink to get the full 1.5 amps.


Cheap low power fans (added 11/3/2015)

Low wattage 12 volt fan:

0.12 watts, 50 cubic feet per minute, under $11. This would be for a regulated 12 volts since the data sheet says 17 volts max and some panels will exceed 18 volts.

Lots of other fans are available at

Cheap Duracell Batteries:

D cells for under $0.70 etc.

Step 5: See Also.... (More Energy Saving Ideas)

Check out my LED light bulb video: LED Light are good but not great. My bathroom light should ast 30 to 40 years.

This video looks at the engineering shortfalls of most off the shelf screw in LED light bulbs.

Perhaps I will do an instructable and redesign one.

See also these instructables.

LED Lighting: One "Dead" D Cell at a Time:

Super Size Your Battery Run Time: D Cell Battery Packs: