I carry 18 and 22 Ah AGM batteries, cheap ones. Ub12180 and the UB12220, 35 and 47$ respectively at the time of purchase.
The 18 could start my 2 week unstarted 5.2 liter v8 engine when new, but just barely, and in warm ambient
I mostly have them for portable 12v power sources, Lights, fans, inverter powering some 120 vAC powertools.
While I try and recharge them to full ASAP, after any use, sometimes it is not convenient, and i do not want to leave them in parallel with other batteries.
I have what is referred to as an Ideal Diode. Most Diodes drop 0.4 or 0.7 volts, which slows and extends charging batteries to such levels as to basically insure they never get fully charged and sulfate and die prematurely.
The Ideal diode only drops 0.04v across it, @ 40 amps. Mine is rate to pass 50. I have exceeded that, for quite a while.
I use 45 amp Anderson powerpoles as connectors,
so in my case... regular engine battery---45APP->diode.....45APP.......> Ub12180/Ub12220
Every time I drive the alternator can charge the UB12180, and once the vehicle's voltage drops below that of Ub12180( which rests at over 13.0v for a week+, they are no longer in parallel, and loads on the starter battery cannot draw from the ub12180.
If jumping the engine battery was required, I could just remove the ideal diode, and return it after engine starting to recharge what was taken from it.
The ideal diode could insure the additional powerpsorts or even cheapo AGM battery you desire as a backup cold weather booster, is charged every time you drive, and you dont have to worry about its own self discharge making it useless for if and when you might need it.
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If you search Ebay and Amazon you can try looking for 'high rate' AGMS, which might or might not be any battery than the regular UB/UPG AGMs.
Odyssey makes some small TPPL AGMS, lots more CCA and cycleability and much less self discharge than the cheapos, but 3x more $$.
I Think a good strategy for long term cold weather airport parking is stuffing the largest AGM one can in engine compartment, but a booster AGM can be Kept inside the cabin or trunk, kept fully charged with the diode is another good option.
I've parallelled my Ub12180 and UB12220 to start a built, high compression SBC that sat unstared for a 11 months with stereo memory having sucked it to 1.88v. They together, had no issues, by themselves, but it was warm outside.
The Odyssey pc680 is nearly the same dimensions as the UB12180 and UB12220
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I've started my v8 through a pair of 45 amp anderson powerpoles, 180+ amps, 90 per connector, no issues, but I stuff 8awg into them. The 45s say 10 awg max.
other anderson connectors are not called powerpoles but can accommodate much larger size cables, upto 0000.
there are generics.
Genuine are better, but the generics mate with the genuine and are not horrible, but not worth the small saving in prices, IMO.
The 45s are a bit tricky to crimp without their special crimpers, the 30's basically any dimple crimper can manage.
XT 60 connectors are also respected by some, but good soldering skills needed.
