Update BatteryState.msg

[borongyuan]

Add ternary lithium battery to power_supply_technology.

[clalancette]

I'm not really familiar with battery chemistries in general, and ternary in particular. Can you provide some links that talk about it?

[borongyuan]

Lithium iron phosphate battery and ternary lithium battery are the two most common types of power batteries in AGV/AMR and electric vehicles. If not subdivided, they can all be counted as lithium polymer batteries (POWER_SUPPLY_TECHNOLOGY_LIPO). When I was working on a driver for a BMS recently, I found that it supports both battery types with slightly different handling. I think it can be handled a bit more explicitly in sensor_msgs, although it may not be of much use at the moment. It might be useful for later more advanced features, such as battery modeling in RMF.
Both battery types have their pros and cons, and you can find plenty of comparisons and discussions about the two. This is a relatively concise article.
https://ferkart.com/lifepo4-vs-ternary/

P.S. POWER_SUPPLY_TECHNOLOGY_LIFE stands for LiFePO4 right? So we don't have to add another item for it.

[gbiggs]

@borongyuan Can you please add a short version of that explanation to the interface definition as a comment?

[tfoote]

Adding this looks good, with some more documentation in the comments for clarity.

[borongyuan]

I have added definition for constants. Hope my understanding of the original contributor(@tfoote )'s definition is correct. I also added lead acid battery. Although this is an older, even somewhat outdated technology, it is still widely used.

[clalancette]

This looks good to me; thanks for adding the extra comments!

[gbiggs]

Thanks for the contribution!