In trying to recharge a fully-discharged Redtop battery, I find that my old Shumacher battery charger is pinning the amps meter full scale, running for a minute or two, then dropping to zero amps and showing a green light for a charged battery. What I suspect is happening is that it is going into a thermal shutdown condition. The charger has a 10-amp setting and a 2-amp setting, and a 50-amp "starting" setting, but it's never been all that useful for starting, since it really doesn't kick enough juice.
I'd like to buy a high quality charger for occasional use that won't break the bank. I don't need a giant unit suitable for a shop, but I need something bigger than 10 amps. What say ye?
It isn't your charger. It's the Optima
Optima support said:
Recovery Option #2: The DIY Solution
This is a recovery method for the do-it-yourselfer using the equipment you've got in the garage. With this option, you're going to trick your traditional charger into charging the deeply discharged AGM battery.
Here's what you need:
Battery charger (under 15-amps)
Jumper cables
A good battery, preferably above 12.2 volts. (It can be an AGM or flooded battery, it doesn't matter.)
The seemingly dead, deeply discharged AGM battery
A voltage meter
A watch or timer
Now, here's what you do:
Hook up the good battery and deeply discharged AGM battery in parallel – positive to positive and negative to negative. Do not have the charger connected to the battery or turned on at this stage.
Now, hook up the good battery to the charger. Turn on the charger. The charger will "see" the voltage of the good battery (hooked up in parallel), and start providing a charge.
After the batteries have been hooked up for about an hour, check to see if the AGM battery is slightly warm or hot to the touch. Batteries naturally become warm during charging, but excessive heat may be an indication that there really is something wrong with the battery. Discontinue charging immediately if the battery is hot to the touch. Also discontinue the process if you hear the battery "gassing" — a hissing sound coming from the safety valves. If it's hot or gassing, STOP CHARGING IMMEDIATELY!
With your voltage meter, check back often to see if the AGM battery has charged to 10.5 volts or above, this generally takes less than two hours with a 10-amp charger. If it has, disconnect the charger from the wall outlet and remove the good battery from the charger. Now, connect only the deeply discharged AGM battery to the charger. Turn on the charger and continue until the AGM battery reaches a full charge, or until the automatic charger completes the charge process. In most cases, the AGM battery will be recovered.
^ exactly. i have done this every year on my summer car as it kills my red top oiver the winter and i am too lazy to install a float.
-J0N
Or, the other option is the optima is junk as the past 5 (2 purchases, 3 swaps under warrenty) or so have been for me..
My cheap Walmart Schumacher charger has an AGM setting.
Hmmm. Interesting. I probably would have tried the above method if I had known about it. But I didn't. So through dogged determination, I have the AGM up around 11.60 volts, and will soon see if it starts the RX-7, which of late has been driven very little.
I thought I bought the red top a year or two ago, but much to my surprise, when I dug into my files for the receipt, I was shocked to find it dated April of 2011! So it's done alright by me, given that the car sits for long periods.
Oh, BTW, I'm still interested in a charger recommendation. 
It does seem that just about everything reasonable has the Shumacher name on it, but some review rather poorly. But not nearly as poorly as the H-F ones! It would be nice if someone made one larger than the little portables, but not so big as the wheeled ones, which are regularly criticized as being big, nearly empty cabinets with sub-par chargers in them.
