AGM Batteries

Submitted: Tuesday, Jun 30, 2009 at 23:00
ThreadID: 70287 Views:2972 Replies:3 FollowUps:6
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Is it possible to "top up" AGM's ? I have a ?Fullriver (Grey) one been under the bonnet for about 2 yrs in my 79 series and about 1 yr in Hilux and suspect it has got very hot a some time as there is some white acid powder-corrosion around the lift out lids. I lifted them but saw the caps/Valves? and did not proceed any further.
I expect it has boiled a bit of the acid out so the question about topping up.
Rob Mac
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Reply By: Member - Phil G (SA) - Wednesday, Jul 01, 2009 at 08:52

Wednesday, Jul 01, 2009 at 08:52
"Lift out lids"...... Doesn't sound like an AGM.
Are you sure its not one of those maintenance free wet cell batteries?
Got a photo?
AnswerID: 372575

Follow Up By: Member - Robert M (QLD) - Friday, Jul 03, 2009 at 19:02

Friday, Jul 03, 2009 at 19:02
Hello Phil, my reciept says "Fullriver"and on the side says"Fullriver Valve Regulated Rechargable Battery HGL80-12". I thought these are AGM's On the top it has a lift out lid lengthways and under it has what looks like caps but I thought it may be the valves so was unsure and left them.
Rob Mac
FollowupID: 640191

Follow Up By: Member - Phil G (SA) - Friday, Jul 03, 2009 at 23:29

Friday, Jul 03, 2009 at 23:29
When you said it was grey, I thought it wouldn't be a fullriver because they are black.
But it is an AGM! and should look like this:
FollowupID: 640220

Follow Up By: Member - Robert M (QLD) - Saturday, Jul 04, 2009 at 00:59

Saturday, Jul 04, 2009 at 00:59
That is what I have. Have removed the carry handle as they are a nuisance and put it back on when I need to lift it out. That strip lenghtways on top can be removed. I think I will leave it and see how it goes on my next trip, will be driving almost everyday.
FollowupID: 640227

Follow Up By: Member - Phil G (SA) - Saturday, Jul 04, 2009 at 09:53

Saturday, Jul 04, 2009 at 09:53
Gday Rob,
You were right when you said the underbody heat has caused it, but the Full River AGMs are current limited, and I expect yours has been getting way too much current. A maximum charge current of 16amps is listed in the specs for your battery:
HGL-80 specs

To explain:
#1 Temp under the bonnet is greater than 25 degrees, and a warm battery has a lower internal resistance and will take a lot more current than a cold battery. Your alternator's regulator has limited temperature compensation.
#2 Your voltage will be regulated at just over 14 volts most of the time. Even if the battery were cold, at this voltage, the current would probably get up over the 30 amp mark if the battery had been used overnight.
#3 Your batteries sit next to one another under the bonnet - the cabling is very short - there is pretty much no voltage loss, so the AGM gets full voltage and max current.
#4 You live in Qld - warm temps shorten the life of any battery.

For the reasons above, I only ever put conventional cranking batteries (never Calcium or maintenance-free) under the bonnet - usually Exide Extremes or Century Overlanders.

An AGM is best in the back of the truck so it never gets warmer than the ambient temp, and the longer cabling required to reach it, will limit the maximum current that can be delivered.

The limited charging current is the downside to the cheaper AGMs and is usually responsible for their early death. 16amps is really low. The 100Ah Remco is a cheapy, and is allowed 30amps. The more expensive AGMs have no limit.

Sorry I have no clues on how to fix your battery.

FollowupID: 640247

Reply By: Member - John M (NSW) - Wednesday, Jul 01, 2009 at 08:56

Wednesday, Jul 01, 2009 at 08:56
I have 3 x 120amp Deep River AGM batteries and they have no caps or valves.
Are you sure you have AGM batteries.

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AnswerID: 372576

Follow Up By: Member - Robert M (QLD) - Friday, Jul 03, 2009 at 19:03

Friday, Jul 03, 2009 at 19:03
Hi John, see my reply to Phil above.
Rob Mac
FollowupID: 640192

Reply By: trainslux - Wednesday, Jul 01, 2009 at 15:19

Wednesday, Jul 01, 2009 at 15:19
You can add distilled water to it, but only in a small amount each time, as it takes a while for the moisture to be reabsorbed into the matting.

Remember reading about a chap who was restoring his agm a while back, and the top cover revealed a series of small caps to the individual cells. Once removed, he couldnt see any moisture, and neither would you.
He added tea spoon amount each day for a while till he was satisfied that it was ok.

Hey if its borderline in condition, you have nothing to loose.

AnswerID: 372641

Follow Up By: trainslux - Wednesday, Jul 01, 2009 at 22:27

Wednesday, Jul 01, 2009 at 22:27
Cant find the old article about it, even after some time searching.
You could add some water to it, like topping up a normal battery amount, and leave it for 4 or so days, then recharge, and test it, to allow the water to reabsorb into the matting.

What happens if its been heated, and thus vented, is that the moisture in the glass mat, does indeed vent, and the matting looses some of its packing or bulk, and the battery looses its ability to work as well, as the electrolyte is less effective.
Adding water allows this to swell, and work as its intended.
Alot of refurbished batteries have this done to them.

hope this helps.

FollowupID: 639948

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