AGM Batteries, they need a decent charge

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.

Jim.

Jim,

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.

PAUL

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 http://www.batteryfaq.org/ and explains things about batteries very well.

Regards

Paul

Greetings

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.

Regards

Paul

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.

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.