I am happy as a clam when my Telecom surplus DEKA 150ah AGM acid rich 1.300 SG battery sits for a couple of months completely disconnected, sitting at 12.88V to 12.86V, depending on temps in the garage. Thick, thick, thick plates, lucky to charge at much over 21 amps, supposed lifetime of 10 years, warrantied for 8 years.
I make sure, as soon as I get back from any trip, to immediately give it 14.4V for 3 to 4 hours, until the Amperage take rate gets down to 0.75 amps... that 1/2 of 1% charge rate that shows it's fully charged, for proper storage purposes. I fully intend to get that 10 years out of it, God willing.
Added a 150W polycrystal 8.33amp portable aimed solar panel and pwm adjustable charge controller set at 14.4V, and it gets near topped off adding 25-40 amps, daily, if the sun shines a bit. System is working fantastic so far. 6 days down at Quartzsite, and I never needed the Honda generator fired up to recharge. Sun went down around 6 pm, I aimed the panel 2x during the morning and that was it... get back at 7 to 8 pm, and Voltage in the battery would be sitting at 12.77 to 12.80 every night on the battery, with almost everything shut off except fridge and parasitic draw items. Most mornings saw 12.60 to 12.66V, depending on how much TV and how long I ran the heater at night before going to sleep.
The beauty of a solar panel is that during the day time, your parasitic loss is being covered by the solar panel at 14.4V, and drawing less amps than it would at 12.6 to 12.8V, so you only lose 14 to 16 hours of parasitic draw amperage in the winter time when dark, to be picked up by the solar panels, instead of 22 hours, with a generator and charger.
