1/2 amp trickle charger enough to keep today's cars over long New England winter?

I have a car I don’t drive in winter. So, I am trying to get a trickle charger for the battery. I see good prices on a 500mA charger at HF. Would that be enough to keep the battery topped up over the New England winter? I am thinking the 500mA charger actually puts out 1/3 amp or about 350mA. I am asking the question, because today’s cars have all kinds of electronics that suck power out of the battery.

I wouldn’t get a HF trickle charger. Instead I’d get a ‘Battery Tender’, about $60 at Amazon. It monitors the battery, doesn’t overcharge it.

To me, it’s better just to disconnect the battery and let it sit for 6 months…Float charging a lead-acid battery can be just as hard on them as letting them self-discharge 30 or 35% over the winter…Store the battery clean and in a cool place (unheated) and it should be fine for 6 or 7 months…Longer than that, the “tender” is probably better HF has those too…

My vote is for the “tender”.

I would agree with the tender idea. Thats what they do. Some on here say it is very bad to disconnect the batteries on current model cars. As far as HF goes, I would never trust anything electrical coming from them. Is it UL rated? I’d be very concerned about defective electronic parts and fires. A fire in a garage is no fun.

I use a battery tender even on my lawn mower.

The charger/tender that I would recommend is the CTEK 4.3 which is currently selling for $59 at Amazon. It received five stars from 110 Amazon customers.


It bulk charges to 80% full charge at 4.3 A (hence its name) then charges with declining current to full charge. If left connected. it then goes into float charge mode (constant 13.6 V) for ten days. It next goes into pulse charge mode, charging when the battery voltage drops below 12.7 V and turning off when the battery reaches 14.4 V. It repeats this cycle indefinitely.

CTEK is a Swedish company. The charger was designed in Sweden and manufactured in China. Its quality is high.

BTW, my engine-off parasitic current drain is 8 mA (2005 Honda Accord). That is fairly low. Drains of about 25 mA are common.

My Schumacher Battery Companion maintains about 13.5V and a 10 to 20 mA charge rate. A cheap trickle charger will overcharge and deplete the water.

I agree with everyone else.

Get a Battery Tender.

Disconnecting the battery can cause all sorts of problems depending on the vehicle.



Make, year, model? Always helpful in giving detailed answers…Newer “luxury” models loaded up with electronic toys can indeed lose all their memory settings if you disconnect the battery. Today, it’s more than just resetting the clock…

Another cheaper alternative is a simple trickle charger connected to a household timer set to come on an hour or two per day.
The basic trickle chargers will not drain the battery when the timer is off.

"My Schumacher Battery Conditioner maintains about 13.5V and a 10 to 20 mA charge rate. A cheap trickle charger will overcharge and deplete the water."

15.3 V is the point at which outgassing begins to occur. Water molecules disassociate into hydrogen and oxygen and those gases form bubbles on the plates.

Acid will separate out in the electrolyte and sink to the bottom, and water will rise to the top of a cell in a wet battery that sits for a period of time without being recharged. This reduces the effective plate area of the cell. Charging the battery afterward may not completely remix the acid and water.

The more expensive “smart” chargers (such as CTEK) have an optional, user-selectable recondition mode that applies about 15.5 V for up to eight hours to cause outgassing at the plates and remixing of the electrolyte. In wet cells with removable caps, depending upon how long outgassing has occurred, water may be needed to be added to replace the escaped hydrogen and oxygen gasses.

My replacement Bosch battery in my 4-cyl Honda Accord is a completely sealed (i.e., no removable caps) flat-plate AGM battery. Water cannot be added. The battery has a “safety” spout at one end of the battery that would release the H2 and O2 gases should the internal battery pressure exceed about 2-3 psi. If the gases are prevented from escaping the battery, they will eventually recombine to form water.

Battery manufacturers (there are only two in the US, Johnson Controls and Exide, and Exide is now in bankruptcy) provide data sheets which specify allowable float voltage and cycle voltage (max alternator recharge voltage). Below is a data sheet for my Bosch AGM Group 51R battery.

Note that the spec sheet lists my Bosch battery capacity as 45 Ah at the 20-hour discharge rate. That is, it can deliver 2.25 A for 20 hours before the battery dies (ist kaputt! as the BMW tech might say). The discharge time at any current draw can be computed from the capacity in Ah. For example, my simple OE radio draws 1 amp. I could calculate how long I could listen before I would need to call for a jump. Because effective battery capacity is greater at low discharge rates, I could play my 1-amp radio for a lot longer than 45 hours. It’s an interesting calculation which I’ll discuss sometime.

What would the OP lose by disconnecting a fully charged battery and letting it sit? Radio presets, yes, but anything else that’s really important to the ability of the car to start and run, or inconvenient to have to reset? If the radio reset code is known and can be entered come spring when the battery is again hooked up, wouldn’t that suffice?

If the car is for sure going to sit undriven, consider suspending some or all of your auto insurance on that vehicle for that time period.

@shanonia - read this:

I made a trickle charger that puts out slightly more than 12.8 volts. Holding it there is what I prefer doing.

Yep just read the article provided by Tester or Texases for problems with battery disconnect. Computer memory loss, shift points, fuel mixture, radio security code, etc. etc. Its copyrighted so can’t be cut and pasted. You just have to go read it.

Agree with others that a Battery Tender from Amazon is the way to go.

pep boys has a good selection of chargers too. fairly cheap. they have all sorts of useful functions.

I just don t like buying things sight unseen.

Interesting article, Tester and Texases. Looks like, for some cars, unhooking the battery can open Pandora’s box.

I’ve never noticed anything other than loss of radio/clock presets. If there were driveability problems I did not feel them. But my newest vehicle is a 2007 Town and Country. I replaced the battery on it, and on my 1999 Honda, as well as several earlier vehicles, sometimes using a 9V battery backup, sometimes not, no big problems. Maybe the newer, and/or more complex, and/or more expensive the vehicle, the greater the possibility of newer, more complex and more expensive problems.

What would you do nowadays for those jobs, such as welding, replacing alternators and starters, opening gas tanks or fuel lines, and any other job that has always had disconnecting the battery as an important safety precaution?

I agree with keeping the battery in the car and hooking up a float charger. Be sure you get a float charger and not a trickle charger. I’d would also suggest one of between 1.25 amps and 2 amps. I don’t think the .5 amp will work, not because the capacity is too low but because of the cheaper materials used to make it.