Batteries, lithium is the way to go

As far as I’m concerned, lithium is the way to go. However, they have their strong and
weak points and like everything else in life it’s a trade off.

  1. Lithium batteries don’t like being charged like lead acid batteries. They hate a float
    charge which lead acid chemistry demands. This means that once the batteries are
    charged you have to completely stop the charge. This can be done by either having the
    charge controller stop charging or drop it’s output voltage so low that no current flows
    into the batteries. This would mean a “float” voltage below 13.2 volts.

This also suggests that a simple automatic relay charging system off your vehicles
alternator and battery system is not a good solution. No control. They charge when the
engine runs and stop charging when the engine is off. They have no way of monitoring
the state of charge of the battery.

If you want to charge off your vehicle’s electrical system then you’ll need something like
a Sterling Battery to Battery Charger. Ones that accommodate custom charging profiles
run between $300 and $400 dollars.

  1. You can’t tell the state of charge by the voltage of the batteries. The voltage of lead
    acid batteries slowly drop from about 12.8 to 11.8 and this tracks very well with their
    state of charge. Lithium on the other hand will sit between 13.2 and 12.8 (depending on
    the current draw) and then suddenly go to zero - at which time the battery is ruined - not
    good. You will need to purchase a battery charge monitor to have any idea how much
    power remains in the battery. I recommend a Victron BMV-702 or BMV-712. The 712
    has bluetooth capability so you can monitor your battery from your phone. I have the
    702 which meets my needs.
  2. Lithium batteries can’t be discharged 100% - like leaving the headlights on and the
    battery goes completely dead. This will destroy the battery as the weakest cells in the
    battery will go into reverse voltage mode and won’t recover. Ching the cash register for
    a new battery. You need some sort of monitor so that when the battery voltage drops
    below 11.5 volts the battery is totally disconnected from all loads. This requires a
    Battery Management System or BMS - either external or built into the battery itself.
  3. Lithium batteries can’t be charged when their temperature is below freezing. If you
    do, lithium crystals will precipitate out of the electrolyte and the battery will be
    ruined. Ching the cash register for a new battery. You can draw power from the battery
    when it is cold, you just can’t charge it. You’ll need a BMS - either internal or external to
    the battery to manage this.

Lithium has several strong points, not the least of which is that it can sit for months
without being charged (as long as no current is being drawn from it) and it will be just
fine. A lead acid battery will be pretty much ruined after a couple of months if it doesn’t
have a constant float charge.

Lithium can be discharged down to 20% and then back to 100% around 2,000 to 5,000
times depending on the battery’s specific chemistry, average temperature, and average
depth of discharge. They should last 10 - 15 years or more if managed properly. Lead
acid claims 500 charge cycles (only down to 50% discharge) but most only get a couple
of hundred and have to replace the batteries every 2 - 3 years.

OK, so what does all this mean to you. Battle Born batteries are expensive - around
$1,000 for 100ah battery. About half this cost is for the lithium cells that make up the
battery. The other half is for the complex and robust Battery Management System that
takes care of over charging, low voltage disconnect, charge disconnect when freezing,
and other fiddly lithium things. You still need a proper lithium charger, but most of the
things that can destroy a lithium battery are taken care of by the BMS.

You may not think you need much power but I’d suggest a minimum of 200 ah, or two
Battle Born batteries, three would be better. I’d also suggest a minimum of 300 watts of
solar (600 would be better) and a good solar controller. Going price for 300 watt panels
is around $200 each. You can get three 300 watt panels (900 watts total) and a
MaxxAir or Fantastic fan on the roof of a 159 Promaster.

Here’s where we purchased our last solar panels. Good prices. I like Canadian Solar
or Longi brand solar panels. Good compromise between price and performance. If you
want top of the line and are willing to pay about 50% more per panel then LG or
Panasonic are the way to go.

For a lot of current battery information I recommend you follow Will Prowse on
youtube. He has the most up to date information on putting together a DIY lithium
battery system. He tests and rates the various batteries, chargers, solar controllers,
switches, and monitoring systems. He’s done such a good job that I just refer people to
him rather than try to duplicate the information he provides.