Best battery tender for AGM

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My vehicle gets parked outside 24/7. I do not have access to any outlets. Is there a decent battery tender you guys can recommend? Thanks
 
If you don't have any outlets, how you going to use a battery tender?
 
Originally Posted by ZeeOSix
If you don't have any outlets, how you going to use a battery tender?


All battery tenders require an outlet?

How about the solar ones?
 
the best way to tend your battery is regularly going on a long drive with a healthy alternator.

isolator switch in conjuction with a charger is an acceptable alternative
 
On a modern car I wouldn't recommend disconnecting the battery as you will lose adaptive learning stored in the modules. Transmission shifting, seat memories, idle learning, not to mention radio presets. If it's a car without a CAN the go right ahead.

A solar charger would be fine. Many manufacturers use them in the storage facilities after import before delivery. AGM batteries handle deep-cycling better than flooded anyway.
 
Originally Posted by Olas
the best way to tend your battery is regularly going on a long drive with a healthy alternator.

isolator switch in conjuction with a charger is an acceptable alternative

Originally Posted by LotI
On a modern car I wouldn't recommend disconnecting the battery as you will lose adaptive learning stored in the modules. Transmission shifting, seat memories, idle learning, not to mention radio presets. If it's a car without a CAN the go right ahead.

A solar charger would be fine. Many manufacturers use them in the storage facilities after import before delivery. AGM batteries handle deep-cycling better than flooded anyway.


On most modern vehicle, the alternator does not fully charge the vehicle to 100% state of charge.

My AGM is showing 12.2V when I checked it in the morning. My vehicle is stock with no add-ons. Nothing modified. Vehicle was bought new. Only 1 yr old.

Can you recommend a decent solar battery maintainer?

I see on the solar battery maintainer, it uses the cigarette light. However, what if the vehicle does not power up the cigarette lighter when the engine is off? How can it charge the vehicle?
 
I suppose the answer to your question is: "Wire it the way you need it to be wired". You'd need to find a wire which is always hot or fit a plug to your battery wiring and use that point to connect your solar charger.

I'd rig a 2 conductor wire to my battery's posts/clamps with a plug on the end and run it into the car. Fit the corresponding plug to the solar charger's output cable.

Are you in a location where vandalism or theft is less likely to occur?
 
Originally Posted by Kira
I suppose the answer to your question is: "Wire it the way you need it to be wired". You'd need to find a wire which is always hot or fit a plug to your battery wiring and use that point to connect your solar charger.

I'd rig a 2 conductor wire to my battery's posts/clamps with a plug on the end and run it into the car. Fit the corresponding plug to the solar charger's output cable.

Are you in a location where vandalism or theft is less likely to occur?


The solar battery tender on one end that has the 2 clamps that goes onto the battery and the other side of the solar battery tender it has a cigarette plug. So, on the cigarette plug, am I suppose to plug it into the cigarette light to get the main battery to be charged?

I do prefer it to not be obviously protruding out
 
The OBD port always has an always-hot pin. Find an adapter to let you back-charge through it.
 
Originally Posted by eljefino
The OBD port always has an always-hot pin. Find an adapter to let you back-charge through it.


Is this really a thing ? I would be concerned about putting any significant power through something that takes very lower amperage. Even if it worked, any accidental short at the OBD connector risks causing significant damage to the ECU, wiring etc.
I have seen small battery dongles that preserve the memory for stereo etc., but again that is low power.
 
I have a 100 watt 'flexible' Sunpower solar panel which can fit behind my windshield, without any shadows from the wipers.

On top of the windshield near noon I measured 87 watts into my depleted battery through a MPPT solar controller.
Immediately after, At the same exact angle behind the windshield, I measured 43 watts and this tapered to 37 watts as the panel heated up 15 minutes later.

This is actual data, not opinion.

Any solar panel charger/maintainer behind the windshield needs to reduce the potential expected wattage by ~50% over its claimed rating, and this is at noon at 32 north. Lesser sun angles will be worse.


ALL lead acid batteries take a lot of time to complete a true full charge. The closer the battery is to full charge, the slower it charges.

Getting an 80% charged battery to 100% charged, takes no LESS than 3.5 hours, and this assumes the battery is held in the mid 14 volt range for that 3.5 hours. It also assumes the battery is still relatively healthy. Less than healthy batteries take longer, and in some cases significantly longer before they reach full charge. The lesser the voltage( electrical pressure) they are held at the longer it takes to fully charge them, and less than healthy batteries might never be able to reach full charge at voltages less than the mid 14 range.

Your vehicle's voltage regulator , wherever it is located, whether inside ECM or internal to alternator or on firewall( rare nowadays) is NOT going to hold the battery at this voltage for that long, even if you were to drive that long, so saying the best way to achieve a fully charged battery is a long drive, is incorrect, and helps contribute to batterycide, and collective ignorance of what a lead acid battery needs to remain healthy for as long as possible.

Determining a true full charge is easy with an Ammeter or a hydrometer or both, but no one ever does it, instead assuming that a battery which can still start an engine is fully charged or nearly so. This collective ignorance drives up battery prices for all of us, and wastes resources. Ideally the lead acid battery is always fully charged and kept cool. Anything less than this ideal is detrimental to the battery. The lower the average state of charge, and the higher the average battery temperature, the faster it degrades/ loses capacity and cranking amperage ability.

An AGM can only be positively determined to be truly fully charged, when the amperage it accepts at a higher voltage, tapers to a prescribed level. when a 100 amp hour capacity AGM battery accepts 0.5 amps or less, when held at 14.4 to 14.7v range at 77f battery temperature, only then can it be considered truly fully charged.

Maintenance free flooded batteries are similar but prefer voltages upto 15 and amperages to taper to nearly zero.

Regular flooded starting, marine/dual purpose, and true deep cycle flooded batteries are more like 1 to 3% of their amp/hour capacity, where the AGM is 0.5%.

An AGM cannot be determined to be fully charged via an ammeter when held at lesser voltages.

Green 'full charge' indicators on Smart chargers do NOT indicate a battery is fully charged, only that the charging source has decided to drop to 'float/maintenance' voltage. They usually drop to float around 92 to 95% charged when the battery is newer and healthy and as it ages or it would be lucky to achieve this level. How much charging still occurs after it is held at float voltage depends on the specific battery, its health and temperature and specific float voltage requirements and how long it is held at float voltage. An Ammeter is extremely revealing.

Most AGMS say the proper maintenance/float voltage is in the 13.6v range, where as wet/flooded batteries say 13.1 to 13.2v range. Holding an AGM battery at too little a float maintenance voltage for long periods, is not doing it any favors. Odyssey AGM says outright if you cannot float it at 13.6v at 77f, do not float it but disconnect it from any charging source and recharge it on a regular basis instead.

Any charging of a less than fully charged battery is better than leaving it at a lower state of charge, but achieving a true full charge is the best way to insure best possible longevity and performance during that life, and achieving a true full charge is time consuming and requires the battery be held at a proper voltage for a proper amount of time.

Anybody choosing to confirm a true full charge with observations of actual tools to do so, will be disappointed with their charging source's ability to achieve this especially on older batteries or those cycled deeper, intentionally or otherwise. But ignorance is bliss, and loves company.
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Ciggy plugs and receptacles, 12v power ports are horrible unreliable electrical connectors, even if one has a receptacle that remains live after the key is removed from ignition.

The SAE 12v connectors are better, but can wear out quickly and become intermittent or highly resistive. They also have to be either input or output and plugging two inputs together, or two outputs together, results in a direct short and perhaps the magic smoke escapes.

I make use of Anderson Powerpoles, and while these are not perfect, and not inexpensive, and require some crimping skills with regular crimping tools for the 15 and 30 amp versions, or special crimpers for the 45 amp versions, they are much more reliable and can handle much more current and many more connection and disconnection cycles before they wear out, they claim 10,000 under load.

XT60 connectors are also reliable low resistance electrical connectors and much less expensive, but require good soldering skills.

IT is entirely possible that a small solar panel can overvolt / overcharge any given battery. There is a lot of bad information online regarding the requirement of a solar controller when the solar panel is tiny. There are many variables to this, and many uninformed inexperienced opinions stated as absolute fact.
A small panel behind a windshield on a vehicle with a considerable parasitic draw is unlikely to overcharge, but it is also unlikely to ever achieve a true full charge or be able to maintain it there.

https://www.youtube.com/watch?v=z5RtZe9AW2E&list=UUoPqTkOluQsuu3RpGnxVwFw&index=9


Lots of solar product 'kits' designed to be put on one's dashboard are extremely overpriced and underperform badly. One can often buy much more capable components individually, for less, but some DIY skills are needed and likely some dedicated fused wires need to pass through firewall to the battery.

It can also be taken to ridiculous extremes in the attempt to achieve perfection.
'Good enough' is subjective, but achieving a true full charge, is not.

The Lead acid battery, whether sealed or AGM or Gel or flooded, all want to be truly fully charged and kept cool, always, and will live an exceptional lifespan if they achieve this ideal.
 
Wow...I am loss for words. That is a lot to digest. Thank you for your wealth of knowledge. In short terms, solar chargers are not reliable.

So in my case, what can I do? I mean do I have to take the battery into the house and charge it? Lol.

Although that is not my desired goal. What other options do I have?
 
Originally Posted by painfx
Originally Posted by Olas
the best way to tend your battery is regularly going on a long drive with a healthy alternator.

isolator switch in conjuction with a charger is an acceptable alternative

Originally Posted by LotI
On a modern car I wouldn't recommend disconnecting the battery as you will lose adaptive learning stored in the modules. Transmission shifting, seat memories, idle learning, not to mention radio presets. If it's a car without a CAN the go right ahead.

A solar charger would be fine. Many manufacturers use them in the storage facilities after import before delivery. AGM batteries handle deep-cycling better than flooded anyway.


On most modern vehicle, the alternator does not fully charge the vehicle to 100% state of charge.

My AGM is showing 12.2V when I checked it in the morning. My vehicle is stock with no add-ons. Nothing modified. Vehicle was bought new. Only 1 yr old.

Can you recommend a decent solar battery maintainer?

I see on the solar battery maintainer, it uses the cigarette light. However, what if the vehicle does not power up the cigarette lighter when the engine is off? How can it charge the vehicle?


If you're seeing 12.2v overnight, I'd say something isn't quite right in your charging system.

Reality is that alternators lack the control to truly fully charge, but Ohm's law doesn't disappear, so they can charge your battery to near full in enough time, like hours and hours of continuous driving. Anything else is a long and slow process and that's where a solar unit will fail, is that it's likely it will never get enough time on, and if it does, it will take days most likely. Meanwhile every parasitic working against you, is.

But we're not a submarine main storage battery, a hospital UPS, or even a telecom tower backup power system. We're talking a car battery, which will fail, and which you'll never have sophisticated enough capability to cycle and count coulombs and amp hours. So perfect is the enemy of good enough here, and if you spend all sorts of effort dealing with the complexities, you'll still be swapping out the battery after a while as a way to mitigate risk.

So if you have no mains power, but can leverage solar, please do so. Don't expect miracles, but every little bit helps. If you can get the battery on a real charge overnight or for a few days even, that would be good,

My suspicion is still that something is wrong with your charging system.
 
I did not say solar was not an option, Solar can be a great option, as it has the time required to actually reach full charge, if the wattage of the panel through the glass is sufficient, and the sun shines for sufficient duration. Even if well undersized, any additional charging is better than no charging of a depleted battery. I just see the products marketed in AP stores are way overpriced for the wattage of the panel, and this wattage is then cut in half by the windshield, At least my windshield it is, I don't have data on every windshield, or even a new one for that matter.

Many vehicle's charging systems today do not try and fully charge the battery, they want to keep it in the 80% charged range so that it can accept higher amperages when the voltage regulator goes from 12.8v to 14.8v. They do this to squeeze out some extra fractional MPGs and boost their fleet average, like thinner oils do for CAFE. they do it at the expense of battery longevity, but they don't get fined if the battery takes a premature dump, and the execs still get their bonuses.

My dad leased a 2018 Cadilliac and it behaved this way, and when I put my powersupply on his in trunk AGM battery, after he got done with a long drive, it required 11.5 amp hours and 3.5 hours, before amperage tapered to what I considered full. He turns in the lease in a month, still the same battery. It lasted the warranty, but I bet it is not a very healthy battery compared to when it was new.

AGMS very much dislike partial state of charge cycling. More so than flooded batteries. They really want to be returned to a true full charge regularly or they will sulfate and lose capacity and performance much more quickly than they would if returned to and kept at very high states of charge.

AGMS can still retain enough CCA to be able to start an engine when they are quite sulfated, as honestly it takes such a tiny fraction of the capacity of the battery to start an engine in this day and age of stop/start and fuel injection.

How much are you willing to spend to prolong the life of your battery? How much is a new battery. What is the new car warranty regarding the battery?

The return on investment could be quite poor.

If you want to do it You need a panel of sufficient wattage that half its rating is acceptable, solar charge controller, and sufficient length of wire to reach the battery and a fuse at the battery. The solar controller will not appreciate being disconnected from the battery while the panel is still in direct sun. Likely not instant failure, but cumulatively damaging to it..


Just did a quick amazon search, there is a dokio 20 watt kit with a solar controller for 33$. The controller they show, I actually have, and one can find it on Ebay for under 8$. It is bare bones chinesium, with the worst and clunkiest user interface known to man, but it prevents overvolting the battery, but it will not drop to a float/ maintenance voltage, it just seeks one voltage and holds it if it can attain it with the wattage available.

I use it with my 100 watt sunpower panel and will get about 5.8 amps maximum from it March to September. I set it to 14.8v and just hook it to various parked/sitting vehicle batteries, and aim panel at the sun for a few hours a day every few weeks or a few days in a row if the battery is quite low.

the 20 watt panel is not very small, and it is unlikely to be able to make more than 17 watts once it heats up outside and is aimed perfectly at the sun. If behind a windshield that 17 watts is likely down to 8 or 9 watts maximum the 2 hours on either side of solar noon.

8 watts at 13.2 volts is 0.6 amps. a group 24 battery is about 75 amp hours of capacity.
4 hours of 0.6 amps would theoretically return 2.4 amp hours of capacity into the battery.

Its not much, but its not nothing either, and it should be more than enough to offset the overnight parasitic draw, if you park facing south in a sunny environment.

Regarding 'flexible' solar panels, consider them bendable a certain limited amount and a flexed a limited number of times. They scratch easily and can get damaged if unsupported and propped up against something. Leaning a large panel against the inside of the windshield and having teh visors hold it up, it will likely not last very long before the cell interconnects break at the stress points. The hotter a solar panel gets the less wattage it will make, so baking in a closed up car is not going to make them happy and achieving half their rated wattage is likely very wishful thinking.
 
Originally Posted by JHZR2
Originally Posted by painfx
Originally Posted by Olas
the best way to tend your battery is regularly going on a long drive with a healthy alternator.

isolator switch in conjuction with a charger is an acceptable alternative

Originally Posted by LotI
On a modern car I wouldn't recommend disconnecting the battery as you will lose adaptive learning stored in the modules. Transmission shifting, seat memories, idle learning, not to mention radio presets. If it's a car without a CAN the go right ahead.

A solar charger would be fine. Many manufacturers use them in the storage facilities after import before delivery. AGM batteries handle deep-cycling better than flooded anyway.


On most modern vehicle, the alternator does not fully charge the vehicle to 100% state of charge.

My AGM is showing 12.2V when I checked it in the morning. My vehicle is stock with no add-ons. Nothing modified. Vehicle was bought new. Only 1 yr old.

Can you recommend a decent solar battery maintainer?

I see on the solar battery maintainer, it uses the cigarette light. However, what if the vehicle does not power up the cigarette lighter when the engine is off? How can it charge the vehicle?


If you're seeing 12.2v overnight, I'd say something isn't quite right in your charging system.

Reality is that alternators lack the control to truly fully charge, but Ohm's law doesn't disappear, so they can charge your battery to near full in enough time, like hours and hours of continuous driving. Anything else is a long and slow process and that's where a solar unit will fail, is that it's likely it will never get enough time on, and if it does, it will take days most likely. Meanwhile every parasitic working against you, is.

But we're not a submarine main storage battery, a hospital UPS, or even a telecom tower backup power system. We're talking a car battery, which will fail, and which you'll never have sophisticated enough capability to cycle and count coulombs and amp hours. So perfect is the enemy of good enough here, and if you spend all sorts of effort dealing with the complexities, you'll still be swapping out the battery after a while as a way to mitigate risk.

So if you have no mains power, but can leverage solar, please do so. Don't expect miracles, but every little bit helps. If you can get the battery on a real charge overnight or for a few days even, that would be good,

My suspicion is still that something is wrong with your charging system.


You are suspicous of the alternator not doing it's job? It is charging a little over 14V.

Ever since the COVID19, I have been driving less. I also think the battery was never fully charged to 100% since new like most vehicle. Since the alternator is to prevent overcharging, and never full charges.
 
Originally Posted by painfx
Originally Posted by JHZR2
Originally Posted by painfx


On most modern vehicle, the alternator does not fully charge the vehicle to 100% state of charge.

My AGM is showing 12.2V when I checked it in the morning. My vehicle is stock with no add-ons. Nothing modified. Vehicle was bought new. Only 1 yr old.

Can you recommend a decent solar battery maintainer?

I see on the solar battery maintainer, it uses the cigarette light. However, what if the vehicle does not power up the cigarette lighter when the engine is off? How can it charge the vehicle?


If you're seeing 12.2v overnight, I'd say something isn't quite right in your charging system.

Reality is that alternators lack the control to truly fully charge, but Ohm's law doesn't disappear, so they can charge your battery to near full in enough time, like hours and hours of continuous driving. Anything else is a long and slow process and that's where a solar unit will fail, is that it's likely it will never get enough time on, and if it does, it will take days most likely. Meanwhile every parasitic working against you, is.

But we're not a submarine main storage battery, a hospital UPS, or even a telecom tower backup power system. We're talking a car battery, which will fail, and which you'll never have sophisticated enough capability to cycle and count coulombs and amp hours. So perfect is the enemy of good enough here, and if you spend all sorts of effort dealing with the complexities, you'll still be swapping out the battery after a while as a way to mitigate risk.

So if you have no mains power, but can leverage solar, please do so. Don't expect miracles, but every little bit helps. If you can get the battery on a real charge overnight or for a few days even, that would be good,

My suspicion is still that something is wrong with your charging system.


You are suspicous of the alternator not doing it's job? It is charging a little over 14V.

Ever since the COVID19, I have been driving less. I also think the battery was never fully charged to 100% since new like most vehicle. Since the alternator is to prevent overcharging, and never full charges.


Charging system can be your alternator, but also the conductors. And there could be a parasitic draw someplace.

12.2V is low after just sitting overnight, yes, low use and short tripping will deplete it more, but 12.2 is still low.

How confident are you in your meter? Ive observed 0.1v differences between obd port, cigarette lighter, and the battery itself.
 
If the alternator is charging at 14v it can still be the alternator?

What other conducters, example?

Could possibly have a parastic draw but I doubt it.
 
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