Battery Chargers vs. Maintainers

[tahoe healey]

I have used a trickle charger for years with no problems. I just read an article about using a battery maintainer. What are the forum's judgments about which is best?

I have my charger on all the time I'm not driving it. This has probably been discussed in the past, but I could not find the thread.

 

[Michael Oritt]

Inexpensive automotive chargers are used for putting relatively high volumes of charge into a battery fast and though the amount of charge may reduce it does not shut off entirely, running the risk of overcharging or burning up a battery. These are not intended for continuous use or connection.

Battery maintainers are designed to deliver a relatively small amount of charge and will shut off when the battery is at full charge, Unlike bulk chargers, maintainers may be left connected continuously when a car is not in use, thus avoiding damage

The best chargers--usually designed for marine use with permanent installation and attachment via wires versus alligator clips to the battery terminals--will sense when a battery is fully charged and then go over to maintenance. The smartest models will also put in a high rate of charge on a periodic basis to reduce sulphating. Needless to say these marine models are way more expensive than either automotive chargers or maintainers and way beyond the needs of the casual driver.

If a car is driven frequently, as in every two weeks or so, neither charging nor maintaining should b necessary. Otherwise it's good to have both a bulk charger and maintainer or tender on hand.

I have a Battery Tender which I can plug into a small two-pole receptacle I mounted through the forward bulkhead of the boot, which is wired directly to the battery.

 

[Bob_Spidell]

Maintainers are 'smarter' than trickle chargers. I once had a trickle charger over-charge a battery and make a mess (maybe it was defective). I think at least some trickle chargers, possibly that one, are constant current* sources, which will keep pushing nominal current--usually 1amp--even if voltage rises which causes an overcharge (all chargers are a type of electrical power supply). I never used that charger again, though they're OK if you watch the battery's state of charge and disconnect it when it reaches 13V or so.

A maintainer will trickle charge until the battery reaches its normal state of charge, then it will maintain a 'float' charge, periodically charging when the battery's voltage drops off (batteries self-discharge over time). Some claim to be able to resuscitate a 'dead' battery; when lead-acid batteries age they will deposit lead sulfate in the bottom of the case. Eventually, the sulfate will short out cells and the battery will lose available power. The maintainer will pulse a higher voltage in an attempt to dissolve the deposits; they seem to work on a marginal battery but some are beyond repair.

I have several BatteryMinder lead-acid maintainers I've bought over the years and had good results with them. The first couple were heavy for their size, which to me means they were analog; i.e. they used a transformer to step-down the AC input to 15V or so AC, then they use a rectifier circuit and a capacitor to give reasonably smooth DC current. The last one I bought was light; presumably it uses a more modern DC-DC converter instead of a transformer. I had problems with voltage regulators for my BJ8 and one overcharged my battery and made a mess (tank out, baking soda slurry everywhere, etc.). I bought an AGM battery and a battery minder AGM charger for it; it seems to work perfectly. The main competing brand is BatteryTender; I'd expect it to be equivalent and I haven't heard anything negative about them. You should check the electrolyte level periodically when on any charger (if the battery isn't sealed).

Side note: Measuring voltage alone doesn't tell you much; a failing battery can hold a charge until you need it. Load testers tell you a little more but these days the parts houses will use a digital tester which will tell you, among other things, the internal resistance of the battery. Worth the investment IMO:

https://www.amazon.com/ANCEL-BA101-Professional-Automotive-Motorcycle/dp/B01M0ARG3X/ref=sxin_16_pa_sp_search_thematic_sspa?content-id=amzn1.sym.44176409-a507-4684-9fe6-68e5d09ea23a%3Aamzn1.sym.44176409-a507-4684-9fe6-68e5d09ea23a&cv_ct_cx=battery+tester&keywords=battery+tester&pd_rd_i=B01M0ARG3X&pd_rd_r=9d5a1a68-8603-4a5f-85a0-ad050cd52c37&pd_rd_w=NKxuS&pd_rd_wg=sE1MZ&pf_rd_p=44176409-a507-4684-9fe6-68e5d09ea23a&pf_rd_r=J4XSR26BQQ02JN7ERT94&qid=1698762047&sbo=RZvfv%2F%2FHxDF%2BO5021pAnSA%3D%3D&sr=1-1-2c727eeb-987f-452f-86bd-c2978cc9d8b9-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9zZWFyY2hfdGhlbWF0aWM&psc=1

* > Constant Current vs Constant Voltage Output <

 

[Tiger37]

I have used a battery maintainer on my MG for years we had an auto electrician come and talk at our Club night years ago. He explained the difference as in previous reports. The battery maintainer I use is similar to the type installed in caravans where charge to the 12v system is constant when on a caravan park. You can set the type of battery and the charge rate.

 

[John Turney]

I use a maintainer, brand BatteryMINDER. I don't leave it on all the time, but I don't have a Smiths electric clock. Any idea how much current the clock draws? If the clock is a new electronic one, it won't use much at all. The old

I do have a MH with almost all the new Ford chassis computers, radio, etc. that constantly draw some power, as well as electric steps that deploy every time we open the side door. They also retract when we close the door. About ever two months. I plug the BatteryMINDER into a 12V power port. I takes less than a day to refill the battery.

 

[Editor_Reid]

I have used a trickle charger for years with no problems. I just read an article about using a battery maintainer. What are the forum's judgments about which is best?

I have my charger on all the time I'm not driving it. This has probably been discussed in the past, but I could not find the thread.

I have used Battery Tender "Junior" chargers for close to 20 years. The number in use at any one time has varied from two (now) to probably 12 or so (when I owned a lot more cars than I do now). In that time two have failed. You know they fail because they go from steady green light to a flashing red light. Simply discard the failed until and attach a new one. I've never had one of them do any harm.

I like that they are simple, inexpensive, and easy to understand:

Steady Red Light - The battery is charging. This is what you see when you first connect it.
Flashing Red Light - Attached incorrectly, or, if attached correctly, the unit has failed.
Flashing Green Light - The battery is nearing full charge
Steady Green Light - The battery is fully charged.

Even I can understand them.

 

[tahoe healey]

I currently have a Schumacher trickle charger. The green light says it is charged (I'm guessing when charge is completed). A yellow light comes on when first plugged in. It goes off in 30 seconds. I'm guessing I can monitor the charging and turn off and on as needed. As stated above, I have had it on all the time with no problem in 20+ years.
I investigated Battery Tenders on-line and there are a lot to choose from. If I decide to convert, what specs should I choose? They are all over the place with price. My latest battery (3+ years) is sealed so I have no clue about the battery condition. The voltmeter indicates a good charge.

 

[Bob_Spidell]

Voltmeters won't tell you much; a dying battery can show fully charged and crap the bed when you hit the starter, or die with no warning. Battery condition testers will tell you more (see above). There's solid recommendations here for BatteryMinder and BatteryTender; I have three of the smallest/cheapest BatteryMinders on three cars right now, and a more expensive AGM one on the BJ8. When I first starting using BMs (heh) they were about $25; this looks like a 'deal'--closeout maybe--but they'll probably get you on shipping:

https://www.northerntool.com/products/batteryminder-plus-battery-charger-trickle-charger-desulfator-12-volt-1-amp-model-12117tc-167981

 

[tahoe healey]

Thanks all, good information.

 

[Bob_Spidell]

ps. With a BM--presumably, with BT as well--you can infer a battery's condition by how long it takes to charge to float level (from solid green to flashing LED). A new, mostly charged battery will go flashing over a few hours or overnight; if it takes a couple days the battery was heavily discharged--normal if it's sat for a couple months--or possibly on the verge of dying. I tried charging a dead battery, and it wouldn't go to flashing, even after a week or so.

 

[Michael Oritt]

I use a BatteryTender Plus (shown)--I believe it has an output of 1.25 amps which is more than sufficient to maintain a full charge.

Because the battery is not accessible on two-seaters without removing the spare I pulled some #12 wires from it to a two-terminal receptacle mounted in the bulkhead which provides for easy connection of the unit.

I also carry a Weego N44 compact jump starter which plugs into the same inlet. Frankly I have had to use it but it seems like a good concept!

BTW the red removable key is for an aftermarket disconnect switch mounted between the battery and ground. It replaces the standard switch which is so prone to failure.

 

[JHaydon]

Firm believer in Battery Tender. I've used the Plus as above as well as the Junior, never any problems. The Junior has lower maximum amperage output so it will take longer to recharge a low battery, but for maintenance there's very little difference.

Also +1 to monitoring battery health by watching the LED. When I was racing I'd always note when I plugged in the Tender and when the light went green.

FWIW, I'm sticking with Battery Tender even though my employer stopped carrying them (couldn't compete with Walmart, Amazon, etc) and now I get an employee discount on the very fine OptiMATE line of smart chargers. Some OptiMATE models are good for 24/7 maintenance (read the instructions) but some higher-capacity models specifically warn you to check the condition of certain size/type batteries weekly to avoid boiling dry. (Having said that, I do have three OptiMATE chargers in my garage and I do use them whenever they're the appropriate tool.)

 

[John Turney]

I currently have a Schumacher trickle charger. The green light says it is charged (I'm guessing when charge is completed). A yellow light comes on when first plugged in. It goes off in 30 seconds. I'm guessing I can monitor the charging and turn off and on as needed. As stated above, I have had it on all the time with no problem in 20+ years.
I investigated Battery Tenders on-line and there are a lot to choose from. If I decide to convert, what specs should I choose? They are all over the place with price. My latest battery (3+ years) is sealed so I have no clue about the battery condition. The voltmeter indicates a good charge.

If you have the trickle charger connected to the battery, the voltmeter will be reading the voltage of the trickle charger. That's why it won't tell you if the battery is bad. If you disconnect the trickle charger, the battery will have a "surface charge" that will last a while before it drops to the actual battery voltage. With a good battery, it will take about a day to drop to 12.6 VDC, the 100% charged voltage of a lead-acid battery at 70F.

 

[Michael Oritt]

Further to what John says, trickle chargers do what their name says: they keep on charging if at a low rate, and unless one monitors the level of electrolyte in the battery cells it is possible to burn the battery up.

In part, because it is inconvenient to access the battery on my 100 I use a BatteryTender as shown in post #11 above to maintain a charge during periods of inactivity. If I need a charger or jumpers I attach the hot lead to a terminal with a rubber shield I have mounted nearby the starter.

 

[tahoe healey]

In checking Battery Tenders, what amp would be appropriate. They are all over the place in prices and amps.

 

[Michael Oritt]

TH--

I use the 1.25 amp/hr model as shown in post #11.
I've had it for a number of years and it works for me.

 

[Editor_Reid]

In checking Battery Tenders, what amp would be appropriate. They are all over the place in prices and amps.

I have always bought the least-costly versions. Can't see a reason to pay more. If the thing keeps the battery charged, what else is there? Sure, you can pay a lot more for tender/chargers that reportedly do all kinds of fancy anti-sulfate stuff and deep cycling, etc., but I've never had a Battery Tender harm any of my cars' batteries, and they - both the Battery Tenders and the batteries they keep charged - last for many years.

The model of Battery Tender (which is the brand name) that I use is "Junior."

 

[tahoe healey]

Thanks for the information.

 

[JHaydon]

Battery Tender Junior (wall wart version) is enough if you connect it when the battery isn't discharged, or if you can wait a long time for it to be charged.

If you tend to wait until the battery is a little flat before remembering to connect it (guilty!), then the Battery Tender Plus (or another higher-Amp BT model) will work faster.

This is a voltage graph of my Mercedes battery before and after connecting a Battery Tender Plus. I had left the car sitting for over a month before plugging it in.

Less than an hour to bring it back from "won't start the car" to "ready to go". I think the shape of the charging curve is pretty neat as well. At 9am the next day the voltage stabilizes around 14+V, then at 6pm it drops down to 13.2V and stays there.

 

[gonzo]

I use both battery tender and a solar powered battery trickle charger Solar Trickle