Battery Charger for Deeply Discharged AGMs

[df2x4]

So after some recent issues with my old Schumacher Ship & Shore 10A "Smart" charger falsely reporting a few deeply discharged AGM batteries as "bad," I'm in the market for a new charger. I've been looking at several different options and I think I know what I need to do, but I just wanted to ask the community here for any input prior to making a purchase.

Initially I started looking at newer "smart" chargers. Specifically the NOCO Genius10. 10A at 6/12V with an AGM mode and "Force Mode" that will enable charging even if a battery is too discharged for the charger to detect a voltage. But I started reading some of the one star Amazon reviews and realized that several people were reporting issues with the Genius10 reporting a full charge when the battery was still around 50% charged, especially with AGMs. There were other issues reported as well, including false charging errors on AGM batteries that were still good (same issue I'm having with my old Schumacher).

Considering I use primarily Odyssey AGM batteries, I then looked at their "approved charger list" and found the CTEK MUS 7002. Very similar specs to the NOCO, but 7A instead of 10 and 12V only with no "force" mode. Unfortunately it's $175 US, and the reviews report several very similar issues to the NOCO.

At this point in my research I started looking in a different direction. I have a few Deltran Battery Tenders and they work great for maintenance charging, so I realized I really just need something that will push a lot of power for deeply discharged batteries. Pretty much every "smart" or "automatic" charger seems to have issues with bringing back deeply discharged stuff, so I started checking out manual cart-style chargers with timers. Enter the Schumacher DSR139.

www.amazon.com/dp/B08PQ3RRVY

6/12V, 10/25/50A charging with a 225A jump start option. No computers, no safety nannies, just two knobs to select charging rate and time and an ammeter. For the same $175 that the CTEK MUS 7002 costs I think this will be a much better tool for what I need. I could bulk charge at 25+A and then move the battery over to one of the Deltrans for finish charging/maintenance.

Just curious to see what you all think of this choice and if you have any other recommendations. Ideally I'd like to keep the budget under $200, I really don't want to shell out $500+ for a comparable Associated or Snap-On for something I'm probably going to use once or twice a year at the most.

 

[heskahoka]

I think you are on the right track.
It is great to have a 'dumb' battery charger around the house. I still have my Dad's old battery charger from the 70s as well as newer smart ones for trickle charging.
If you are patient and want to save some money, I see dumb chargers pretty often on Craigslist or garage / estate sales.
The older dumb chargers use transformers instead of all solid state components which makes them pretty bulletproof.

 

[RichLo]

I have an older style of that schumacher but I'm pretty sure its the same internals since its all the same stats and functions. It still wont charge a fully discharged battery, even on 25 amp. It has a function that as a battery gets closer to full charge it will slowly ramp down the output so when its fully charged its only putting out around 2 amps when its set on either 10 or 25 amp setting. Those are just max outputs so 25 for a car battery or 10 amp for a motorcycle or lawnmower battery.

The only way to force charge a depleted battery is to either hook jumper cables up to a good battery then charge the good battery. Or hook up a transformer DC Electrode positive stick welder for a few minutes.

 

[Pinger]

How 'heavily discharged' are we talking here?
My battery flattened a week or so back (a consequence of faffing about with the HVAC controls) to the point it showed 10V (on a separate voltmeter) and all I got was relay click when trying to start the engine. I revived it with an old school charger which showed 2 Amps initially. A standard lead acid battery as far as I know (2 years old).

 

[df2x4]

How 'heavily discharged' are we talking here?

Very. No dome lights, 5-6V on the multimeter heavily discharged.

 

[Scooterwrench]

I've got three battery chargers. A Dayton 6/12V pure manual with 200 amp boost that I've had since the late 80's for car/truck batts,a Exide 12V 6/2 amp. that is regular old charger that I use for smaller batts. and a NAPA smart charger that self determines batt. voltage for doing the smaller 6V batts. The NAPA charger will charge a completely dead batt. but I have to restart it sometimes. I think you're on the right track with that Schumacher boost charger. Like Richlo said sometimes you have to wake them up with a direct voltage injection off a live batt. Just be careful doing that,if the dead batt. is shorted inside it may blow when you hook it up to a live batt. A way to test for that is to strike the cable across one of the terminals. If you get a big arc stop and toss the dead battery.

 

[Scooterwrench]

Very. No dome lights, 5-6V on the multimeter heavily discharged.

5-6V is not totally dead. That NAPA smart charger should bring it back to life. Bad batteries show with weather changes. If it died after a cold snap it's probably toast.

 

[df2x4]

If it died after a cold snap it's probably toast.

The batteries in question have since been charged (borrowed an old dumb charger) and load tested, they're fine. Long story short, this was all brought on by a parasitic draw issue in the Monte Carlo which sometimes sits for weeks at a time. Everything's good now, draw has been eliminated.