Alternatives to APU

[JimT]

Reading the thread about diesel generators got me thinking about alternatives. I know there are at least one, maybe more, battery based APU's out there. Recently I've been thinking about going this route but building my own system to meet my needs. Figured I'd share and see what others have for feedback...


The newest plan is looking like a 2nd battery bank, a maxwell ultra cap, some solar (eventually) like Waterloo has and the smallest A/C I can find that fits my needs. My inverter can take AC shore power to pass through and charge the batteries too. Also need to replace my alternator so I'll be upgrading to something appropriate. I don't spend much time in the truck, 4-5 nights a week at most and home weekends, so I don't need that much power or cooling. Unfortunately the over night load is currently bringing the batteries down into the 12.3-12.6v range and the truck doesn't start as smoothly when it drops below 12.4v Been looking at those LiFePO4 (Lithium Iron Phosphate) batteries recently for the bunk, various different brands. Seems a bit pricey up front but should make sense over the lifetime, especially for my setup. I've only been getting about 1.5-2 years out of a set of "deep cycle" AGM's with my usage habits and the LiFePO4 should last significantly longer.

Right now I have 4 deep cycle/starting AGM batteries, about 15 months old. I think one is going bad and I plan to swap it for the maxwell cap. I'll keep the 3 good AGM's to run the truck and act as a backup to the ultra cap and add a second bank with the LiFePO4 batteries just for the bunk, Inverter and AC. Probably wire in a manual switch to connect the AGM's to the bunk for emergencies. Eventually I'll add the solar, more as a failsafe to keep the batteries charged if the truck sits for an extended vacation or something. Keep the fridge cold.

Only real downside to the LiFePO4 batteries is the charging/discharging temperature ranges. Typically discharge -4F-140F with charging between 32F and 140F. I've seen some with built-in heaters, but with 3ish months of 32F and below temps where I am it's something to carefully consider.

I like to take my time thinking about things and get feedback from others before I put a plan like this into motion. And yes, I realize this solution wouldn't be much savings over other options, but it would be lighter, more compact, quieter, and more fuel efficient (?) than a generator. It would also be tailored to my own needs and fully serviceable by myself.