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Best battery tender for AGM #5388320 03/28/20 10:27 PM
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painfx Offline OP
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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

Re: Best battery tender for AGM [Re: painfx] #5388332 03/28/20 11:11 PM
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ZeeOSix Offline
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If you don't have any outlets, how you going to use a battery tender?

Re: Best battery tender for AGM [Re: ZeeOSix] #5388342 03/28/20 11:30 PM
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painfx Offline OP
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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?

Re: Best battery tender for AGM [Re: painfx] #5388344 03/28/20 11:34 PM
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Originally Posted by painfx
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


Without any outlets, I'm guessing you're just going to disconnect the battery and bring it inside for charging? Here's a cheap 8 amp charger for $25.02.

https://www.amazon.com/Schumacher-SC1279-12V-Rapid-Charger/dp/B07DM22XTN

Re: Best battery tender for AGM [Re: painfx] #5388358 03/29/20 12:04 AM
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I've used the solar ones, they actually worked pretty decent but it wasn't an AGM, I used it on a lead acid battery.



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Re: Best battery tender for AGM [Re: painfx] #5388393 03/29/20 04:23 AM
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Olas Offline
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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

Re: Best battery tender for AGM [Re: painfx] #5388505 03/29/20 09:34 AM
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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.


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Re: Best battery tender for AGM [Re: LotI] #5388532 03/29/20 10:20 AM
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painfx Offline OP
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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?

Re: Best battery tender for AGM [Re: painfx] #5388555 03/29/20 10:46 AM
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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?

Re: Best battery tender for AGM [Re: Kira] #5388597 03/29/20 11:46 AM
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painfx Offline OP
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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

Re: Best battery tender for AGM [Re: painfx] #5388645 03/29/20 12:58 PM
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The OBD port always has an always-hot pin. Find an adapter to let you back-charge through it.

Re: Best battery tender for AGM [Re: eljefino] #5388739 03/29/20 03:10 PM
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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.

Re: Best battery tender for AGM [Re: painfx] #5388830 03/29/20 06:03 PM
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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.
-----------
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.



Re: Best battery tender for AGM [Re: painfx] #5389025 03/29/20 11:27 PM
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painfx Offline OP
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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?

Re: Best battery tender for AGM [Re: painfx] #5389032 03/29/20 11:59 PM
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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.

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