Battery charger question

[onanysunday]

So my wifes Audi has a big H7-AGM battery in the back of the car. Bought less than a year ago from Auto Zone. Their supposed best AGM battery. Anyway we leave the stereo on and it shows 7.6 volts. I try my battery tender and also a 12amp Schumacher smart charger. Neither one touches it. They supposedly charge it back to 100% at Autozone in about 90 minutes. He told me they have a "big charger" in back for dead batteries.  I really need to buy a good roll around charger with some power. What do you guys like and why?

 

[Kraut_n_Rice]

Your chargers are probably not working because the battery voltage is too low for it to be "seen".  Smart chargers are a pain if the battery is truly dead.  Try putting another charged battery, or one of those small jumper boxes, in parallel with the dead battery.  It should bring the source voltage high enough for the charger to kick on.  I've had to do this a few times..

 

[r3meyer]

Yeah the smart chargers need it to be "Jumped" if you want to get them rolling.  

Try to find a NOCO charger.  If you can find a G26000 those will charge anything.  Including LiFePo4 @ 24amps.  They will also charge a battery from completely dead.  You can also use it as a 12v power source if you want to test things.  Cant say enough good things.  The new version is $500 so try and find the G26000

https://www.ebay.com/itm/294275246426?epid=1372400157&hash=item44842be95a:g:eQYAAOSwjbJg7Opp

I paid $200 for mine.  

 

[onanysunday]

I actually had to jump with another battery to the positive and negative post under the hood to get the trunk to open. Guess I could have just left it connected and put the charger on it and charged it. Interesting

 

[Realbadlarry]

most of the nocos have a force charge where you can send voltage to a dead battery, it will then charge it correctly.

 

[wopachop]

 He told me they have a "big charger" in back for dead batteries.  I really need to buy a good roll around charger with some power. What do you guys like and why?

I like using modern RC car chargers because theyre cheap and really smart and adjustable. The adjustability allows you to turn them into old school dumb chargers. Works good for the situation you describe when a 12v battery is down at 7v.