AGM Batteries, they need a decent charge

Submitted: Tuesday, Feb 08, 2005 at 21:44
ThreadID: 20258 Views:25674 Replies:6 FollowUps:5
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I have a Lifeline 100 amp AGM Battery that has performed very well but needs a charge from a decent source other than the alternator from time to time to get it up to peak capacity.

It has been sitting in the car for the last three weeks getting a charge (after a camping trip where it was never at full capacity) from the alternator, but will not get to 100% charged. I have put it on the battery charger with a two stage Projecta charge analyser connected and it is still charging after 4 hours and still may take another 10 hours.

I have also found that after using solar on it it will hold 100% for weeks and then gradually drops back.

My conclusion is that a car altenator wil never charge them fully all the time; they need a serious charge from mains or solar to get to full capacity and then the alternator will hold them at that until they get worked over again.


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Reply By: Member - Jimbo (VIC) - Tuesday, Feb 08, 2005 at 21:54

Tuesday, Feb 08, 2005 at 21:54
I now rescind part of that. Between posting and now, it has slipped into "float" mode. Perhaps 4 hours is all it needs, but this still confirms it was not fully charged from the alternator.

My point is alternators do not fully charge any battery.

AnswerID: 97335

Reply By: Paul - Tuesday, Feb 08, 2005 at 22:25

Tuesday, Feb 08, 2005 at 22:25

I refer to my earlier post 20166 and my comment ......

Quote:-"Only reason I hesitant about Deep cycle is you never get them back to 100% charge when out the middle of nowhere as the require 15-16Volts to charge up to 100%"

Seems we agree about not being able to fully recharge deep cycles off alternators

John AKA Mr Bitchi if your reading this , you commented

Quote:- "Duh?? first time i've ever heard that one......
Cheers, John"

Make that second time in a few days John :-)

Thanks Jim.

AnswerID: 97345

Follow Up By: Member - Jimbo (VIC) - Wednesday, Feb 09, 2005 at 07:29

Wednesday, Feb 09, 2005 at 07:29

I may not have put it well. The AGM charges to about 95% from the alternator, unlike a wet cell DC that will only get to about 80%, so I am not complaining, just noting that it doesn't seem to get totally full.

As for 15-16 volts to fully charge a battery, I disagree. This will bugger a battery. The mains battery charger charges at 14.2 with the Projecta attachment and my solar panel has a regulator fitted (specifically for AGM batts) that charges at 14.1 on the advice from the bloke at Federal Batteries.


FollowupID: 355984

Follow Up By: Paul - Wednesday, Feb 09, 2005 at 08:30

Wednesday, Feb 09, 2005 at 08:30

.......walks away with foot in mouth

FollowupID: 355996

Follow Up By: MrBitchi - Wednesday, Feb 09, 2005 at 11:41

Wednesday, Feb 09, 2005 at 11:41

Thats what I thought...

Cheers, John.
FollowupID: 356031

Reply By: paulpp - Tuesday, Feb 08, 2005 at 22:33

Tuesday, Feb 08, 2005 at 22:33
Greetings Jim

The issue is alternator voltage. AGM batteries require a charge voltage slightly over 14 volts. A normal battery (wet cell sealed or unsealed) requires a little over 13 volts to be fully charged.

Your smart charger/solar brings your AGM up to max charge because it applies correct voltage.

Some newer vehciles which have "calcium calcium" batteries have higher rate alternators (eg later model Land Rover Discoveries) and can fully charge an AGM as a deep cycle battery in a dual battery setup.

Have you alternatoir charge rate checked by an auto electrician. If the alternator is a few years old it can be charging low . This site is a good reference site and explains things about batteries very well.


AnswerID: 97351

Follow Up By: Member - Moggs - Tuesday, Feb 08, 2005 at 23:59

Tuesday, Feb 08, 2005 at 23:59
Yep, agree with that. I get 14.4 volts to my Remco AGM battery in the rear via some 150amp cable off the Redarc and it charges it to 100% every time. I haven't even put it on a charger yet, just leave it in the vehicle.
FollowupID: 355966

Follow Up By: Member - Jimbo (VIC) - Wednesday, Feb 09, 2005 at 07:23

Wednesday, Feb 09, 2005 at 07:23

Car is only 8 months and runs a calcium battery. I'm getting 14.4 volts. It will happily hold at 100% after being brought up to charge. It's only after a workout with the fridge that the alternator won't get it to 100%, it does however get it to about 95% but won't top it right up.


FollowupID: 355983

Reply By: paulpp - Wednesday, Feb 09, 2005 at 08:12

Wednesday, Feb 09, 2005 at 08:12

Probably worthwhile checking out at what battery voltage the second battery charge is stopped at by your dual battery system controller. If this is a little low the battery will not be fully charged. In the case of an AGM gassing must be avoided, so being set on the low side is probable.

My experience is that most dual battery systems are designed around "wet cell" (old technology if you like) batteries and the installation of AGM or similiar batteries that require higher charge rates or are fully charged at a higher voltage than a wet cell battery, results in these batteries not reaching a fully charged status when charged using a car alternator and most dual battery management systems.

Also what actual capacity is the vehicle alternator (amp/hrs). This can also be a factor in whether or not the second battery is fully charged. Your alternator my have insufficient excess capacity to properly manage a second battery.

Having said all the above achieving a 95% charged state may be acceptable in relation to battery life using an AGM. It needs to be discussed with a qualified person.


AnswerID: 97390

Reply By: Member - Sand Man (SA) - Wednesday, Feb 09, 2005 at 08:51

Wednesday, Feb 09, 2005 at 08:51
In most, if not all, dual battery setups, the second battery will NEVER receive a full charge, regardless or whether it is an AGM, Gell, or Wet Cell battery.

the Isolator/Controller is "fooled" into believing the battery(s) have received a full charge as it is detecting the charge state of the Primary battery.

That is my understanding anyway.

I'm diagonally parked in a parallel Universe!

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AnswerID: 97397

Reply By: Mainey... - Wednesday, Feb 09, 2005 at 11:12

Wednesday, Feb 09, 2005 at 11:12
When camping for an EXTENDED period with any auxiliary battery system, either wet cell, sealed, calcium, AGM or Cranking / Deep Cycle the only simple and certain way is to charge is with a solar system, to maintain 100% charge and retain maximum battery life!
Yes, it may initially appear expensive but if you do a lot of camping trips they work and it saves food, tempers and batteries, smaller and inexpensive solar panels do work for 7 to 10 day holidays, as tested and verified here on EO.

When at home, if it's a daily use vehicle, for 100% charge and maintainence to the auxiliary battery system, remove and leave on a ‘trickle charge' battery charger, or similar, (as manufactures use ‘different’ words to describe a similar process) between uses, how long does it take to remove/refit ? ..probably only (10) minutes…
to save battery problems like sulphation, undercharge and discharge etc, that give a shortened battery life and low battery performance.

If it's a weekend only use vehicle attach the trickle charger to the auxiliary battery system during the week for the same result and next your trip you will know you have a fully charged auxiliary battery system.
AnswerID: 97418

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