Without the battery, the van won’t have light, heat, cooking facilities, a water pump, or any of the other things that turn it into a useful place to hang out.
We chose to use a Lithium Ferric Phosphate (LiFePO4) battery. Lithium batteries can take a charge much faster than lead-acid batteries. They also don’t mind being left in a state of partial discharge, and they can be discharged to around 20% capacity without impacting their service life.
Our system came from Balqon in California. It also incorporates a pretty basic battery management system to prevent it from being overcharged or drained too much. Unfortunately, although Balqon’s prices are good, I can’t recommend using them. They are used to dealing with commercial customers. They do not answer the phone or respond to email. Their customer service is non-existent. I wrote more about my experiences on the Sprinter forum.
Update: Looks like Balqon is out of business now. Not really surprising.
I’d be tempted to look at cells from a manufacturer like CALB. Remember – each cell is only 3.2 volts, so you need four in series for a 12v system. Four of the ones I linked to will provide 180 amp hours. Buying eight will give you 360 amp hours, which is probably a good starting point for most people.
Lead-acid versus Lithium
Lead-acid batteries don’t like being discharged beyond 50% of their capacity. They also get upset if they are left at less than 100% charge for more than a day. They weigh a lot more than lithium batteries too.
When you take into account the added usable capacity of a lithium battery, a lithium solution will weigh about one quarter as much as an equivalent capacity lead-acid battery bank. My neighbor Ken helped me place our battery into the box he designed and built. It was easy enough for two people to carry. Each one of the four equivalent lead acid batteries would have been too heavy to easily pick up. That’s a massive space and weight saving for use in a vehicle.
So what are the downsides to lithium? One concern is that they tend to blow up. Boeing had problems with the batteries on their Dreamliner planes. Radio Control plane enthusiasts store their batteries in ammo cans and charge them very, very carefully to prevent them from getting too hot and going into “thermal overrun” (also known as “bursting into flames”). Luckily, LiFePO4 uses a different chemistry to those volatile batteries. It is thermally stable to over 500 degrees Fahrenheit, which is plenty for us.
Lithium batteries also don’t like being charged up in sub-zero temperatures. For us that means keeping the battery inside the living area of the van, and making sure that there’s warmth in the van even if we aren’t using it. Luckily, because the battery only takes up ¼ the size of a lead-acid equivalent, we’re not losing much space inside.
Another big downside is cost. The up-front cost of lithium is about 2x to 4x the equivalent cost of a lead-acid system of the same usable capacity. However, the service life of lithium battery packs is at least 10 years if they are well treated, compared to 3-5 years for lead-acid.
So, if you are prepared to start with a relatively bare-bones lithium system as opposed to one of the overpriced drop-in lead-acid replacement systems, and if you have the extra money to invest in the system up-front, then lithium at least breaks even with and may even cost less per usable amp-hour than lead-acid in the long run.