battery charger suggestions

[gregaustex]

What do you guys use to keep the battery charged through the winter? I'm looking to buy a charger and don't have any first hand knowledge of what works well. Have never had to deal with not driving a car for a season.

Any suggestions, steering me in good direction is appreciated.

[wayne-o]

A battery tender is your best bet as it wont put much charge into yours,any other normal charger will feed a minimum of 2 amps into it and that is simply too much for an unused battery.

[carguy123]

Winter? It's Memorial Day Weekend and you are in Austin, Texas.

You don't have a real winter in Austin, and even if you did, it'd be months and months away.

[gregaustex]

thanks wayne.

car guy - I put winter for the many folks on this board who can't drive their cars for several months. I figured they would have a solution for taking care of their battery through months of storage.

[rx7locost]

Battery tenders are good for this type of use. I went the other way. I just don't use anything. I have had very good success with my past toys by not using anything. In those cars, the battery is 100% disconnected from the rest of the car via a relay in the regulator. For the Locost, I have added a "racing" cut-off switch. When not in use, the switch is thrown and there is no load on the battery. All batteries today will easily store over winter for 6 months with no load without the need for keeping them charged. most modern cars have a minimum load on the car during "off" times, thus necessitating the battery tender for anything more than a few weeks. For example, even an alternator will draw a couple of milli-amps from the battery while at rest. Disconnect the battery and there is only the self-discharge rate of the battery iteslf.

[BBlue]

Battery tenders are good for this type of use. I went the other way. I just don't se anything. I have had very good success with my past toys by not using anything. In those cars, the battery is 100% disconnected from the rest of the car via a relay in the regulator. For the Locost, I have added a "racing" cut-off switch. When not in use, the switch is thrown and there is no load on the battery. All batteries today will easily store over winter for 6 months with no load without the need for keeping them charged. most modern cars have a minimum load on the car during "off" times, thus necessitating the battery tender for anything more than a few weeks. For example, even an alternator will draw a couple of milli-amps from the battery while at rest. Disconnect the battery and there is only the self-discharge rate of the battery iteslf.

Yes indeed! I had a battery retain its charge for at least 2 years. When the project was "completed", it had the oomph to start a 2.0 four banger. Overwinter is a piece of cake for todays batteries.

Bill

[gregaustex]

Bill and Chuck - thanks. I think I will change my desire to ask for a battery tender for father's day to something else.

I pushed my old Mustang out of storage this weekend and the battery of unknown age couldn't muster enough grunt to turn the engine over. Took the battery to Autozone to check it out and it is officially dead. I will unhook this battery to extend the life when in storage next time.

Does unhooking a battery on a old car with a generator, yes, not an alternator, have the same effect?

thanks for the suggestions.

Greg

[rx7locost]

Does unhooking a battery on a old car with a generator, yes, not an alternator, have the same effect?

What? The same as disconnecting on an alternator equipped car? It all depends on what other things are powered, such as solid-state regulator, radio station retention and clocks etc. Disconnecting the battery will kill any electrical presets. If you have the old mechanical station presets, then no. My ol' MGA had no such modern amenities. Plus it had a low voltage disconnect built into the mechanical regulator. Absolutely no cuurent was drawn from the car at all.

Me thinks your major problem is

I pushed my old Mustang out of storage this weekend and the battery of unknown age couldn't muster .....

the unknown age may be the main factor. Batteries do have a finite life. I got 10 years out of my MGA battery and my wife's Buick got 10 years+ and would still be going strong (maybe) if the terminal hadn't rotted away. Disconnecting the battery during storage is a good alternative to installing a cut-off switch.

[maxlessca]

Lead acid batteries will self discharge if left for extended periods of time. It doesn't matter if they are unplugged from everything, they will still loose their charge over time. At my grandparent's cottage, I help them open(end of May) and close (Oct) it up every year. We always disconnect the batteries from all boats and the lawn tractor in the fall. In the spring, every battery needs to be charged, because they will discharge themselves over time. They typically don't have enough power to turn over the engine. All these batteries are less than 5 years old. We are looking into battery tender's this year for each battery. At $35 for the Jr tender, its hard to go wrong. It would be nice for the batteries to just be "ready" in the spring...

[a.moore]

You have to pay attention to what kind of battery you have if you want to use a tender. I bought a sub $10 one from HF after getting good reviews from a few friends.

When I was reading the directions, I noticed that it said "do not use on absorbed glass mat batteries". As luck would have it both the Locost and the formula car have AGM batteries.

I went back to the store to see if they had something that would work with an AGM battery and there happened to be a retired EE that overheard my question. He gave me a very detailed explanation but basically AGM batteries cannot vent like a regular battery and a regular charger may damage the battery.

The formula car has a master switch like Chuck was referring to. Even after sitting a whole winter, the tiny motorcycle battery had no trouble firing the engine. Even if you can't/don't have float charger, disconnecting the battery ground works really well.

[turbo_bird]

If a good battery is fully charged before storage, it should be good for several months if there's no drain on it. A couple years ago I had an old Festiva that sat for about 8 months including -40 for extended periods in the winter. I definately didn't expect it to start without a boost in the spring, but it fired right up. Maybe I just got lucky too.
Kristian

[dhempy]

We always disconnect the batteries from all boats and the lawn tractor in the fall. In the spring, every battery needs to be charged, because they will discharge themselves over time. They typically don't have enough power to turn over the engine.

Then it sounds like you're wasting your time disconnecting them!

-dave "dishonorably discharged" hempy

[rx7locost]

Numbers that I have seen for auto batteries are a self-discharge at between 1 and 5 mA. That is a VERY general number. The warmer the storage, the faster the chemical reaction so the faster the discharge. Storing batteries in cooler places is the best for long term storage. For the sake of discussion, I will use the higher number; 5mA. A typical auto battery might have between 45 and 75 AH storage capacity. There are 24 * 30 hrs in a month. So, worse case, a battery will self-discharge 3.6AH per month with nothing connected to it. In 6 months time that would be 21AH or ~1/2 the capacity of the smaller battery. That seems to be a fair number if the higher rate is used and we store the battery at room temp. The cooler the storage temperature the less the discharge. For winter storage, the self discharge rate is much less than the 5mA used for the above example.

All other things being equal, the higher the capacity of a battery, the faster the self-discharge rate. To look at it another way, one could use a figure of ~5% self discharge per month. So in 6 months, the battery has discharged to 70% (100% -(6 months x 5%)) of its capacity if it was fully charged to start with.

As far as not disconnecting the batteries for long term storage, by all means, disconnect them. You will disconnect any system loads however small they may be. Even a 5mA load (1/2 the current for a typical LED) could double the total discharge. Many diode packs in modern alternators will have reverse leakage at 1-2mA. Add to that the small current draw of its internal electronic regulator. If a battery was originally sized to a specific engine with no fudge factor ( a technical term ) then I can see how long term storage could discharge enough to prevent starting form the slightly discharged battery. Add to that, some engines need to turn the engine over to pump fuel (no electric fuel pump) and you will loose a lot of the remaining battery capacity before fuel is in the carb. Electric fuel pumps are great for starting and engine after long periods of storage. Old tractors had a lever to manually activate the mechanical fuel pump before trying to start after long periods of non-use. 1950's OMC outboards had squeeze pumps in the fuel line for the same purpose.

If a battery is allowed to fully discharge it is difficult to impossible to recover. Plus the electrolyte becomes water when fully discharged and can freeze if stored in an unheated area during winter months. A battery will not freeze if it is mostly charged.

Sorry for the long dissertation.

[gregaustex]

Thanks for the discussion.

Problem is most likely just an old battery. From date code decoding it is 7 years old, I've had the car for five years. Car was not driven much in the last six months due to other work I was doing on the car.

Usually I drive this car once per week or once every two weeks to keep it running well, but some minor resto work over the last half year kept it unusable.