Topic: Leaving Battery Tender Connected in Garage?

[TwoTired]

TT,
Do most AGM battery manufacturers/marketers have those charging specs available ?
                     Thanks in advance for your help 

I can't really answer that as I don't know them all.

Usually, the operational technology is not all that different from a flooded cell battery.  But, different plate metals/alloys ARE possible.
AGM stands for Absorbed Glass Mat.  These mats fit between the plates and just enough liquid electrolyte is introduced to wet the mats which have contact the plates.  The electrolyte is held in place largely by capillary action and inherent adhesion properties, so it doesn't spill.  My AGMs get charged from smart providers of power, either the vehicle on board voltage regulator or an automatic charger with a charge rating compatible with the capacity of the battery being charged.

The charge rating is all about the C rating of the battery.  Say the battery has a 12AH rating, this is the C rating or the maximum safe continuous discharge rate of the unit.  (It's more complicated than this, actually.  But, this is close enough for now).  Normal safe and prolonged charging is done at 1/10 C or about 1.2 Amps in this case (until outgassing is observed).  Charge maintenance of a fully charged battery is usually at a C/100 rate, in this case 0.120 A or 120ma.  This latter charge rate is considered not enough to cause the battery to overcharge/ overheat/ outgas.
3 stage chargers usually cover most of the charge bases.  But, there are 5 stage chargers as well as chargers that adjust their Voltage sensing in accordance with temperature changes.  Cold, fully charged batteries show a lower voltage than Hot fully charged batteries.  If your charger doesn't automatically compensate for temp, you risk undercharging your battery in a cold winter garage with resultant sulfation.

All this is tempered with the standard internal resistance of the battery in question (relates to battery plate materials and assembly construction), which is why you really SHOULD follow the manufacturer's recommendations regarding charge conditions.  If the battery has higher internal resistance, the C/100 rate is augmented to allow for that resistance or loss of charge power for the plate/electrolyte absorption.

Hope I didn't make your head spin.   
There's a lot of info out there about batteries and chargers.  So, it's hard to make it simple without specifics.

[grcamna2]

Ok TT,
I understand the 1/10th,and just learned from what you said about the temp. of the battery being charged(what temp. is optimal?) but I'm interested in reading the battery voltage and seeing when it's necessary to begin charging it i.e. the minimum voltage before a good charge.I would have liked an exact way of knowing when an AGM battery wanted to be charged.I'd also like to know when it's reached full charge and what voltage would be optimal.
I sold a few Yuasa AGM's and they had very good instructions included which took the guess work out of it,but that was a few years ago and I realize that there are many different companies selling them now.

[Stev-o]

I have a tender but don't see the need of keeping it hooked up at all times.

[78 k550]

I leave on on all the time. gell cell.
Goldwing battery's say can take a trickle charge of 2 amps. I can use my car charger on it.
small battery tender is 750ma or 900.

Paul

[dave500]

I don't like things left plugged in,anything can over heat and catch fire especially cheap stuff like timers and chargers,properly looking after a battery is another labour of love,if you flip a few bikes the old battery goes into the seller and the keeper gets the new one over and over,i like lead acid batteries,i used to be the gold coast 24 hour "holler for a marshall"guy over twenty years ago.

[AJK]

Nothing wrong at all with lead acid batteries. Sure they have the weight, but extra weight helps you when your trying to break the sound barrier. They have been around for about 1000 yrs as well.

Actaully, lead acid batteries have an excellent recycle regime. Even though your dealing with toxic/harmful materials, if they are recycled properly through a proper depo, they are recycled in a highly efficient manner with little environmental waste. The lead goes one way, the plastics another. Not sure what happens with the acid? Perhaps it gets neutralised and made environmentally friendly.

I haven't looked into gel-cells much, but they must behave different (better??) on a tender long term? I guess they must because they are used in a lot of high end communications equipment thats always on a power source 24/7. So during a power outage, they take over. So i guess they must work better for continual tender charging.

[dave500]

I think gell batteries are like ethanol fuel,it aint quite right?

[TwoTired]

I understand the 1/10th,and just learned from what you said about the temp. of the battery being charged(what temp. is optimal?)

A given charger should have a specification for the temperature at which its other specifications are derived.  This is typically 70 F.
I've added a chart here of what the typical AGM likes to get vs. temperature.
I got the caution relationship backwards in my earlier post and will go back and correct it.

but I'm interested in reading the battery voltage and seeing when it's necessary to begin charging it i.e. the minimum voltage before a good charge.I would have liked an exact way of knowing when an AGM battery wanted to be charged. I'd also like to know when it's reached full charge and what voltage would be optimal.

14.4 V should be the trip point for switch from equalization charge to float charge.  And float charge voltage should be 13.8V.  Note these voltages are while being fed power by a charger.  The Voltage status for a battery rested and unloaded are the same as for any other lead acid battery.  Second chart below.

Perhaps you are asking about open circuit battery voltage over temperature?  See last chart.

In the end, an AGM is still Lead acid technology, meaning the status voltages are the same as the flooded cell types.  However, just because the electrolyte is somewhat immobile in an AGM they are sensitive to overcharge issues.  If your Vreg or charger tries to maintain the battery at 14.4V in hot weather, it will overcharge an AGM on long cruises or long durations in hot weather.

REF:
http://batteryuniversity.com/learn/article/absorbent_glass_mat_agm
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery


Hope this helps.

[Vinhead1957]

I leave tenders on all my bikes(3). All winter !   I believe they extend my battery life.   2005 second battery 2007 second battery

[grcamna2]

ok TT,  Yes,that does help.
Temp. makes a big difference in the resting state charge of the battery voltage or specific gravity reading ? and the battery(AGM only?) is more prone to overcharging when the temp. rises ?