Keeping a 12V car battery charged? How?

I have a 12V LED strip that I want to turn on whenever the power goes down. I want to power the strip with a 12V car battery, but I don’t know how to recharge and keep it charged. I have used an old computer UPS in a similar situation with excellent results but I wonder if there is a more elegant solution.

Maybe a trickle charger designed to keep car batteries topped off while in storage? Here’s another one.

ETA: If this is for emergency lighting, consider solar charging solutions that can recharge during the day even if the grid is down for multiple days or weeks.

Sounds like what you want is a battery maintainer. You can find them at most auto stores and home and garden centers. Also at battery centers and online.

I use one like this for a seasonal vehicle.
And one like this for my motorcycle.

A small low amperage unit like the second one is probably just fine for your application.

Also, if this is for emergency lighting, consider solar charging solutions that can recharge during the day even if the power grid is down for multiple days or weeks. LEDs aren’t usually very power-demanding. Assuming 10 watts of LEDs and 12 hours of lighting, you’d only need a 120 watt-hour / 10 Ah @ 12V battery to keep them lit all night. Something like a 50-watt solar panel ($200ish with charge controller) should be able to fully recharge the battery over the course of an average day – though if you decide to go this route, do a bit more research so you don’t end up shortening the batteries’ lifespans by cycling through them too much.

Exactly. Unless it’s free (as in an older used one), the car battery may not the best choice for this purpose. It’s not clear if you want this for emergency lighting or for daily use, but either way it’s a low current application. Car batteries are made for delivering very high current for a very short amount of time. Smaller, cheaper batteries designed should meet your needs better, though.

It is for emergency lighting only. My home alarm has a programmable output that can send a signal when the AC power is down. I have connected a 12V automotive relay to the programmabe output and I already have the car battery.

In short, the whole system works, I only need a way to recharge the battery. And since it is an appartment I don’t have a suitable place to put a solar charger.

Here’s a float charger for $10.

For about 6 bucks at Home Depot I bought a thing that looks like a cross between a CO detector & a night light. It’s a plastic block about 2" wide, 4" tall, & 3/4" deep with a standard male 120V plug molded into the back.

it plugs into a wall outlet & contains a battery, a charger, and some LED lights. If the power goes out the light comes on. And you can then pull off the wall & use it like a flashlight.

Mucho simple. Mucho effective.

If this URL doesn’t work, go to and put “288479” in the search box. The price now is all the way up to $9.

I just got one of these:
for my basement flood alarm, and a battery to go with it. I don’t know if it will keep a car battery charged, but they are lead-acid, just like the gel-cells this thing is for, so I’m guessing it will work.