Best deep cycle ?

Skid Row Joe wrote:
If their claim is true, then wouldn't that be a bargain versus the regular batteries?

Yes they can indeed be a bargain ... if you're careful not to make ONE SPECIFIC MISTAKE too often with AGM batteries: Don't put on them too-high float voltages too-long in too-high outside temperatures.

Doing the above on regular wet (liquid) acid batteries does boil the water out of them and can eventually permanently damage them, too. But ... with regular wet (liquid) acid batteries you just have to check the water level in them and top the level back up if you've accidently applied too-high float voltages too-long in too-high temperatures.

HOWEVER ... AGM batteries are sealed with a one-way valve (lets vapors OUT - ONLY) ... so if high charge voltages vaporize some of the water out of them there's no way to replenish their water content. This means that you've damaged them permanently a little bit each time you do it to them.

That's why I like those Interstage 100 amp hour Group 29/31 AGM "wheelchair" batteries -> they're designed to be floated at 13.5 to 13.8 volts - exactly the output range of most RV stock single voltage converters. Stock RV converters don't ruin them by boiling too much of their water away when left hooked up for long periods in moderate or low outside temperatures. However in high outside temperatures 13.5 to 13.8 volts can begin to get into a "too high" range for them for long term float hook up during high outside ambient temperatures ... so I disconnect my converter from my AGM batteries during the summer when outside temperatures are high.

You might be wondering how you can both "charge" and "float" those Interstate batteries on the same 13.5 to 13.8 fixed volts that RV converters put out. Well, the converter does trickle charge them while floating them. However this trickle charging rate is much faster with AGM batteries because of their very low intrinsic resistance, hence they will absorb much higher currents - if they start out being low initially - when exposed to only trickle-charge (float) voltage levels.

My twin AGM 12 volt batteries will shoot up to absorbing 18-20 amps from the converter for awhile if they start out being partially discharged. I could use a multi-stage charger instead of the converter to hit them with 14.XX volts for awhile, but a few hours on only the stock converter usually does the trick. If I need higher power charging I just use the engine alternator for a bit before leaving them on the converter for several hours.

When leaving a drycamping site with our AGMs down 45-50 percent, 4-6 hours of driving time completely recharges them because of the fast charging that results from their natural low internal resistance.

My AGM batteries were a special value because I only paid around $47 each for them when new.