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I was doing some work on the car where I was cranking the engine but NOT starting it. Well, eventually the battery discharged to where the engine wouldnt crank. I thought the battery would last longer than what I was doing. The battery is an AGM group 27 Autolite replica type.

When my Battery Tender Plus ( compatible with AGM batteries ) is attached the red light is on indicating a recharge as opposed to a solid green indicating "maintenance mode".

The battery is currently at 12.75v so does it need recharging and if so, how long would that take the Tender to accomplish?

As a additional question, how do you prevent the battery from discharging when doing a compression check ( or other engine work ) where the engine is always being cranked but not started??

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A fully charged battery should show close to 13.2 volts, so yes, you need to recharge it. How long it will take your battery tender depends on what the output of your tender is. Most battery tenders are designed to maintain a charged battery at full charge, not recharge one. A 2-amp tender will take several hours. A problem with discharging batteries is that the sulfur in the battery acid can coat the lead plates (sulfate), making it difficult to recharge them with a low capacity battery charger.

I have a 10/40 amp automatic battery charger with a 200 amp boost function that I use. I can use the 10 amp setting on AGM batteries or the 40 or 200 amp settings for a short period of time to break the sulfation loose. I also have a 10-amp "smart" battery charger/tender/ that also desulfates, and is more friendly for AGM batteries.

Another thing, a battery with a bad cell can show that it is charged, but won't have any capacity, and discharges quickly. You have to run a load test on it to see it.

Edited by Don C
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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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"The battery is an AGM group 27 Autolite replica type." I accidentally discharged my AGM replica battery, I left the key in RUN too long. I recharged it with an AGM compatible charger. I  had about 1 hot re-start after that with the AGM battery. It now has a regular lead acid battery made by East Penn Manufacturing and sold as NAPA Gold in my area. It actually is made in the USA. It works as it it should. Chuck

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That company, East Penn,  is not far away from where I live.  They manufacture high-quality batteries under many brand names.  My neighbor and my lawn and landscape guy both work there.  It's nice to know that something good is still manufactured in the US.

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I have no idea how I managed to redact the first line of my last post. Maybe it is part of the software upgrade to protect classified information. Chuck

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On 6/19/2020 at 2:29 PM, c9zx said:

I have no idea how I managed to redact the first line of my last post. Maybe it is part of the software upgrade to protect classified information. Chuck

Hiding that secret squirrel information ...   those old work habits are hard to break ... LOL

Ohio Mustang Supply

440-949-2556

 

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  • 1 month later...

I would never leave a battery hooked up to any charger, WHY? It always creates a way to start a fire. I have let my car set of 6 months and not need a charge. I always unhook battery when not driving. At shows and in garage. Better safe than sorry.

 

When a man is in the woods and talks and no women are there is he still wrong??:P

David

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I use battery chargers/trickle Chargers all the time. Three of them...

"Yes dear", has kept me in the hobby a long time...

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SteveO

There isn’t really a fixed amount of time that it takes to recharge a battery.  Lost of variables like discharge, ampacity, specific gravity, temperature, amp rating of charger, etc.

Most battery chargers are targeting a voltage somewhere in the 13.4-14 volt range.  You hook up to a discharged battery and they chug along trying to reach that target voltage.  The higher the amp rating of the charger the faster it can get to that point.  The less discharged the battery is the faster it can get to that point.
 

Battery tenders in my experience are just that- tenders.  They seem to keep the battery at the float voltage (about 13.3-13.4V) and do a decent job as long as you keep them plugged in.  Now If you try to use a tender as a charger It is going to take hours if not days as they only deliver an amp or two.  Kinda like filling a swimming pool with a garden hose- sure it works, but it is a lot faster with a fire hydrant.


As for keeping that stuff plugged in 24/7, it is just personal choice.  The local ford dealership had a nasty fire in a service bay from an F550 they had hooked up to a charger overnight and something went wrong.  That spooked me- so I leave my battery disconnected when not in use.  To each their own, it isn’t like I am pulling the battery cable every night on the wifemobile which is in the garage with the mustang.

 

 

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