Automatic Battery Charger

I need to know if it is safe to use an “Automatic battery float charger”
I usually go away 30 to 60 days at a time, and inevitably when I came back the battery in my car is exhausted. Last year, to the advice of my mechanic I disconnected the negative cable from the battery. When I returned from my trip to Italy, I reconnected the cable, and the engine started with no problem, but the next day…dead! The technichian from AAA recommended an eletric (to be plugged in) automatic battery float charger. (Car is always garaged)
I’m getting ready to go away again, but I’m afraid to use the charger. Is this device safe or it can cause an eletrical fire? Please advice!!!

We usually recommend a “battery minder”, which is a slow charger that automatically keeps the battery topped up. They are not expensive and quite safe.

Sorry, never heard the term “float charger”.

I know this one isn’t super cheap, but I’ve had it for several years. I use it professionally at work and have been very happy with it.
The nice thing about it is that it will also charge a completely dead battery, should you ever leave the dome light on. I’ve successfully charged stone dead group 31 batteries back to full functionality with this tool.
Anyone that knows what a group 31 is, knows that aint some small lawnmower battery.

Docnick…a “float charger” keeps a battery charged at the rate that it discharges. It will not overcharge a battery like a trickle charger. I haven’t heard the term either for about 30 years. I didn’t even realize that they were still sold or utilized anymore.

I have charged a dead group 27 battery overnight with a 2A trickle charger so charging a group 31 with a 125 amp charger isn’t a big deal, but that NAPA charger is a good one if you need a professional grade charger or use one a lot.

@Keith yeah I use it a lot. Several times a week. Our fleet has thousands of vehicles and several shops. “My” shop is responsible for hundreds of vehicles. There’s always some guy that forgot to turn off his lights.

I have a battery maintainer from sears for my boat, $46 5 years ago that works great for me, Though I can ask but a bud of mine had a charger for his boat, battery caught on fire, then gas tank caught on fire, lucky we have a good fire department, toasted boat and garage.

The other option is the obvious one. Disconnect fully charged battery before storage but, Charge it just before you start the car when you return. Personally, I do that with all my boat batteries rather then leave something plugged in for 30 to. 60 days. Assume you have had the battery and car charging system checked too ? My batteries seldom loose much charge disconnected for 30 plus days if they are fully charged to begin with.

@dogosa try 9 months, September till June, MN weather.

Me, I wouldn’t leave a charger on a battery for that long unattended. Certainly not if the battery were inside, where if it caught on fire it would damage something.

Removing the battery before you leave, thoroughly cleaning its top of all acidic residue, neutralizing with some soda water, then storing it (off the car) in a warm dry place will help. You can charge it up with a regular battery charger when ou get back, before re-installing it in the car. That’s what I’d do. I concur w/@dagosa.

It’s sort of puzzling that you came home, the car started fine, presumably you drove it, then the next day it wouldn’t start. That might be the indication of a different problem. Have you taken the car for a battery and charging test at one of those places that do this for free? Might be worthwhile.

“When I returned from my trip to Italy, I reconnected the cable, and the engine started with no problem, but the next day…dead!”

If this battery has been drained empty more than a couple of times and it’s more than a few years old it’s near the end of it’s life.
With a healthy battery disconnecting the cable will work for 6 months or more.

I don’t advise leaving the battery float charging (it is an engineering term) unattended, that’s a bad practice with any kind of battery.

My charger switches to “maintain” mode when the battery reaches full charge.
My charger stops charging if it senses that the battery is defective and/or won’t take a charge.
I’ve charged batteries unattended overnight countless times.
I have never fried a battery.
I have never burned down the shop.
I have also never left a charger hooked up for months at a time.

“I have also never left a charger hooked up for months at a time.”

That’s what I really meant by unattended.

George, these chargers are designed specifically for this type of service. No harm will be done.

The “Battery Tender” brand is well-regarded. I got mine from amazon.

I have both a Schumacher 1.5 amp battery maintainer/charger; cost about 25 bucks and a Harbor Freight float charger that cost about 10 bucks. You do not want to use a ordinary battery charger for long periods of time as it will deteriorate the battery but a maintainer or a float charger will be ok. The Schumacher is a 1.5 amp charger for as long as it needs to be and then automatically goes into maintainer mode. Both work for me; do the job equally well and both are UL Listed. I use them all winter long to keep a couple of motorcycle batteries ready to go in the Spring. They work equally well with car batteries.

UL Listing means that the device has been tested to determine that if it should fail, it will fail safely in a manner that is not harmful to people and property.


So you are saying leaving a battery on a tender is a bad idea? I do not buy it. Why would the lawyers let sears sell a battery tender - maintainer if it did not work? Not to mention the numerous posts on this site suggesting one.

@Barkydog who is your question directed at?

@db4690 any one such as suggested by @circuirtsnith"I have also never left a charger hooked up for months at a time."

@Barkydog I haven’t had reason to leave any kind of charger/maintainer hooked up for months at a time.

I personally never said anything even remotely negative about those battery charger/maintainers.

But others may be hesitant to leave a charger/maintainer hooked up for months at a time.

Everyone has the right to use the tool as they say fit.