backchannel: agm for vandwellers

Part of a response to a question I answered.  OP wanted advice on the short term only, and I’d overshared my thoughts on the long term.  I took it out and moved it here.

If you decide vanlife is for you, in the **long term** the biggest bang-for-buck in deep cycle batteries is 2x 6v golf cart flooded (wet cell) batteries in series, usually 200Ah+. They are able to take massive abuse and can be maintained (watered) when used hard. The purchase price is about half of what AGM cost, and they'll likely last longer in this use case. There are very few *actual* 12v deep cycle lead-acid batteries. The lead plates are so heavy they are not practical for humans to move. Hence splitting them up into two 6v batts. The 12v ones that do exist cluster on the high end: northstar, odyssey, rolls. **AGM weren't developed for our uses**; they were developed to for standby/backup applications where: * normal liquid electrolyte would stratify when sitting still for long periods - this is not an issue for us because our batteries are agitated by vehicular movement. * they could provide massive current suddenly when needed (ie, invert their power to AC to run cell towers when grid power goes out) * would sit fully charged at float voltage (Vfloat) in perpetuity with limited damage Our van battery banks are not still, do not stay fully charged, and generally speaking do not need the ability to dump massive current in a hurry. > > ## exceptions to the rule > > There really _are_ situations where AGM is warranted but they are relatively rare in vandweller scenarios. > > > * the 'dweller installs the battery bank in a location where it is not reachable for normal maintenance > > * the 'dweller needs to mount the battery on its side for some esoteric reason (or is 4x4 trekking so the RV itself can end up in weird angles) > > * the 'dweller chooses to run heavier-than-normal loads like microwaves, electric coffeemakers, electric cooktops, etc. Note this means **the battery can be drained faster** (and bulk recharged faster), not that it provides more capacity. > > * the 'dweller has has a chemical hypersensitivity. > > * the advanced 'dweller is running a single battery for both house and starter systems (["shallow cycling"](http://rvwiki.mousetrap.net/doku.php?id=electrical:solar:shallow_cycling))  <-- not for beginners! >