• running out of power is most often caused by optimism about what loads one can run and how much power one can harvest offgrid
• it can also be related to battery bank capacity.
• rarely it is caused by component failure

(about these summaries)

Before we can fix a problem we have to understand it. In a perfect world we would have realistically assessed the challenges and solutions beforehand but here we are. I am writing this to help you get the lights back on, not to beat you up about how you got here.

Some tools will help with troubleshooting and subsequent addressing of the problem the problem:

• a battery monitor to see what is really going in and coming out of your battery bank
• a multimeter for measuring voltage, continuity, etc.

Folks who live in houses and apartments can run what they want when they want. Vanfolk don't have that option.

So if the lights go out everytime you run a 1500w XtremeFoodNuker<tm> or space heater the answer for most people with average systems the answer is “stop doing that”.²⁾

Sometimes a fix is easy if one can stop wasting power:

• run 12vdc capable loads (like laptops and USB outlets) off 12vdc rather than an inverter. This will save on inverter losses (~20%).
• turn off devices that are not being used

A common problem is overreliance on a single form of charging. Unless done carefully it's a “hard mode” approach. Choosing a charging mix is usually cheaper and more effective.

Another problem is missing opportunities to charge. Having solar doesn't help if the panels aren't deployed, and the alternator can't charge if you have the charging setup disabled. To paraphrase Glengarry Glen Ross, “A. Always. B. Be. C. Charging. Always be charging.”

People want “more battery” to solve their power problems. IMO it rarely does.

• If you are going into sundown without a full³⁾ charge then the problem is likely too little solar harvest (see below) rather than too little battery capacity.
• If you are arriving at camp after driving for hours and not fully charged then the problem is likely too little alternator charging (see below).

If you can run the load in the daytime off solar but not at night then the problem has more to do with timing than capacity. Can you move the load to the daytime when there is excess power? How much is it worth it to you in dollars and effort to run the load at night instead of day?

More battery is the answer if you have robust charging and are trying to increase offgrid autonomy, or if you are bumping into the current limits of your battery chemistry/capacity. Example: if you want to run a 100A load but the LiFePO4 recommended max is 0.5C⁴⁾ then you will need at least a 200Ah bank. Not for capacity per se, but for throughput. Same with charging – if you have a short charging window but lots of current then a bigger bank will accept more of that current.

Battery chemistries like LiFePO4 charge something like 10%-15% more efficiently than lead. Switching to LiFePO4 can make your solar or alternator setup act bigger than it is.

Major gains in solar harvest can be made by:

• installing or increasing panel (everywhere)
• adding tilt (higher latitudes, winter)

Minor gains in solar harvest can be made by:

• replacing PWM solar charge controller with MPPT. Typically an increase of ~15% in solar harvest)
• adding tilt (average latitudes, seasons other than winter)
• cleaning panels to remove dirt/dust, typically an increase of 5%

• replace lead batts with LiFePO4 for an effective increase of ~10% due to improved charging efficiency

A $50 relay can feed the bank more current than a $1000 solar setup while the engine is running.

• add/increase alternator charging with [relay](https://rvwiki.mousetrap.net/doku.php?id=electrical:12v:alternator#combiners) or [DC-DC](https://rvwiki.mousetrap.net/doku.php?id=electrical:12v:b2b) (massive increase when the engine is running)

Externally-regulated secondary alternator setups are $$$ but can yield monstrous power on demand.