Thread: Flat AGM batteries

Originally Posted by drivesafe

Hi John, and you can only try recharging the Optima and see if it is recoverable.

My Range Rover has not turned a wheel in just under 3 years now, but I forgot to take the batteries out and after 14 months, I did so.

The cranking battery, which was just a couple of months old when the RR broke down for the final time, was at 0.7v and I managed to get it back up to a 55Ah capacity. It's a throw-away.

The Optima was also low, can't remember how low and after quite a few recharge-discharge cycles, I have it back to about 60% but it is useable for odd jobs around the workshop.

So give your Optima a few charges and see how it goes.

Thanks Tim. The annoying thing is that, like yours in the RRC, the Optima was only in the car for a couple of months before the transmission went. Wish I'd known the dangers then. It could have been doing service in my D1.

On another note: got my isolator yesterday. Thanks a lot. You can expect a phone call!

Originally Posted by johntins

Thanks Tim. The annoying thing is that, like yours in the RRC, the Optima was only in the car for a couple of months before the transmission went. Wish I'd known the dangers then. It could have been doing service in my D1.

On another note: got my isolator yesterday. Thanks a lot. You can expect a phone call!

Actually, there's a question. Once I replace the isolator with yours, is it worth a try putting the Optima in the aux battery position and letting the alternator have a crack at it? Or can I do harm? The C-Tek has been at it for a while now. It throws an error after a while, unfortunately.

Hi John, try starting your motor and then use a set of jumper leads and give the Optima about 15 minutes on charge with your motor at idle.

See if this brings it up to where the Ctek can charge it.

A slow charge with the Ctek is still the best way to go until the Optima is charged properly.

Good advice.
I have an AGM which was fairly new, but was left unused for about a year. It would not give a reading on my Projecta seven-stage charger.
I plugged a 15 watt solar panel into it and left it for a month. The battery is in an Ark battery box. After a month the meter on the battery box is showing five green lights. However I don't know if it will cope with being put under load.
I intend to leave it on the solar panel until December and, if it is OK, take it to North Straddy camping over Xmas.
We'll see how it goes.

Sent from my SM-G900I using AULRO mobile app

Originally Posted by drivesafe

Hi John, try starting your motor and then use a set of jumper leads and give the Optima about 15 minutes on charge with your motor at idle.

See if this brings it up to where the Ctek can charge it.

A slow charge with the Ctek is still the best way to go until the Optima is charged properly.

I tried 15 mins off the Falcon,, but the C-Tek still brought up an error. So, last night I gave it an hour off the Ford, and then tried again. It's been on for nearly 24 hours now, with the Car, Recon and AGM modes on, and it is nearly up to the green lights. So, I might be on a winner.
So, can someone tell me what is meant by 'float'? Is that just leaving on the charger?

Originally Posted by Trout

I had a few very flat agm batteries. My Ctek charger is a 20 amp jobbie. I also have a little Ctek. Both would not charge them as they need a min battery voltage for the charger to detect the battery. I have used both a cheap charger or another good battery to trick the Ctek into starting the charge.

I tried that, but not with a spare battery, as I didn't have one not in use, so I hooked up one of those lithium iron jump starters more in hope than anything, but nope. Maybe if I had left it longer, but the Optima drained it pretty quickly.

Originally Posted by johntins

I tried 15 mins off the Falcon,, but the C-Tek still brought up an error. So, last night I gave it an hour off the Ford, and then tried again. It's been on for nearly 24 hours now, with the Car, Recon and AGM modes on, and it is nearly up to the green lights. So, I might be on a winner.
So, can someone tell me what is meant by 'float'? Is that just leaving on the charger?

Float is when the battery is fully charged and the charger lowers the output voltage to a rate that will keep the battery topped up without over charging it - usually around 13.7V from what i have seen/read.

Originally Posted by loanrangie

Float is when the battery is fully charged and the charger lowers the output voltage to a rate that will keep the battery topped up without over charging it - usually around 13.7V from what i have seen/read.

Cheers. I kinda thought that was it, but I've come undone with my '40 years ago' training lol. Best to ask.

Anyway. I may have saved my Optima. I sure hope so .