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Batteries, ignorance, dreams

Roadtreking waxes eloquent about the amazing lithium battery system in his RV. It is, perhaps, a better lesson on why snake oils sales so well rather than anything useful about RV battery systems.

First problem is that he is amazed at the kind of power draw you can get from Li batteries rather than the power density. Li is used in laptops and most decent power tools these days because the batteries do have a very high energy density compared to other battery types and Li batteries also have a low internal resistance which means smaller batteries can power larger loads without too much loss in efficiency. As noted in the post, though, these advantages are not free.

Another problem is stepping over the fire hazards as if they have been solved. Boeing could maybe say something about this in regards to their Dreamliner airplaine. Li batteries store a lot of energy and the chemistry needs a lot more care and attention in charging and usage than Pb batteries do. Modern electrical systems can take care of some of this but it is worth keeping in mind that abuse and neglect are the most common cause of short battery life in RV’s.

As for expense, consider that Lithium Batteries (Amazon search) of the sort commonly used to build larger batteries, such as 4Pcs 18650 3.7V 5000mAH Rechargeable Lithium Battery Yellow cost $10 for 6.6 amp hours at 3.7v or about 1.6 amp hours at 14.8v. To get close to a typical group 24 RV battery, you’d have to scale this up by a factor of 50 or so. That means the choice is between a $100 Pb battery at Walmart or $500 for a custom Li battery. Then you can add in the fact that the RV probably already has the charging system for the Pb battery but you’d need another couple hundred to handle the special needs of a Li system.

Another dream item was about these batteries and solar panels becoming effective <em>real soon now</em>. This dream is teased by the fact that prices have indeed come down somewhat. Exactly how far this progress can go is something of a question as it looks like we are in the tail of a logarithmic curve that is flattening out. The promised breakthoughs have been ‘on the horizon’ for many years so the odds of this happening are rather low. Then there are the physical limitations such as solar insolence and its implications that must be considered.

The post notes that half the RV roof had solar panels rated at 600 watts. That’s about $1000 for solar panels plus maybe another $500 for wiring and controllers that will harvest 5 KwH of electrical power on a good day (fifty cents worth of grid power).  

It is a persistent dream but it will take people who know the difference between power and energy and don’t sweep unpleasant cost vs benefit analyses under the rug to make it happen.

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