Battery power utilization.

Important note:
Since the creation of this guide, stats for most power grid related modules were changed. Most notable was solar power nerf: solar panel output were reduced 8 times from 4 to 0.25 while mass remains the same. That means that most numbers in this guide are off (sometimes tenfold). But the general principle did not changed.

Original introduction:
There are many questions about batteries weird behavior, so I did some research.
I believe this matter to be important enough to make a guide instead of discussion.

Summary

1. Batteries always charges in parallel.
   Any surplus power divides equally between all batts in power group.
   
2. Batteries go first in the list of power supplies.
   Whenever demand for energy arises, it go first for batts, and only afterwards to solar panels and generators.
   
3. Most important: Batteries supply power in consecutive order, at maximum rate of 100 per battery.
   Power demand goes to first battery first. If more than 100 energy per tact needed, request goes to second battery in list, and so on.
   Example: If total drain is 150, then first battery will discharge by 100 per tact, and second by 50. Third and following batts won’t discharge at all.

Disclaimer:
I only did heavy testing on small-scale power grids (up to 10 batteries). While I believe my conclusions to be true on any scale, any kind of oddity can occur.

Reference to other guide

http://steamcommunity.com/sharedfiles/filedetails/?id=801547890
Great guide by Mojack. It initially encouraged me to try and build solar powered ship. However, not all of his statements are 100% correct. Specifically about a battery needed 0,3%~0,4 % to start charging the next one. Maybe it was true when he wrote his guide, not now:

• Batteries do not charge each other
  
• Any battery can supply power whatever small amount of charge left in it. Of course, 0%
  charged battery still won’t work.

Practical application

So, how does it work on practice?
Let’s say, we have a ship with 300 permanent power drain (2x small shields) and expected maximum drain up to 1200. Theoretically, 600 power generation + 6x batteries should do the job. 300 power goes into shields and 300 power charges batts by 50 per each.

On practice, the picture will be similar to this screenshot.
What do we see here?
On top display we see total 600 energy generated and… 599 (lol vat?) battery power. Total 1199 potentially available. 599 power looks awkward, but it’s almost 600, right? It should work.

But it won’t work. On bottom display we clearly see that first 3 batteries do not have any charge. That happens because shields drain 300 power not from generators, but directly from those three batteries. 600 power from generators then evenly distributed between 6 batts, 100 per battery.

As a result, first 3 batteries effectively locked at 0%, because they drained at the same rate as they recharged (100 per tact). System displays, that they supply power, but when you step on the pedal, they won’t be of any help. Like on next screenshot.

Now let me show you even weirder stuff.
Same setup, 2x small shields (300 drain), 6 batts, but only 400 power generated. Look at screenshot.
What can be seen:

• 4 batteries not charging
  
• Fifth battery charges at half rate
  
• System states, that we have 466 battery power available.

How’s that possible? Let me explain.

300 power drains from batteries. 400 generated power goes into batts at rate of 66,66 per battery. Power demand goes to first battery, but it can’s supply 100 power, instead it gives only 66,66 power per tact, all it have. Same goes for the next battery and so on. At the end, first 4 batteries supply 266,66 power without charging. Fifth battery supply remained 33,33 power, which is 1/2 of it charging rate.

Since last two batteries do have charge, they can (potentially) supply 200 power. That’s where weird battery power comes from (466=100x2+66,66x4 rounded down).

How to combat it

Best solution I came up to: Exceed battery power by generated power. Since battery can’s discharge faster than 100 per tact, supplying it with more will prevent it from locking at 0% state.

Let’s say, we building solar ship. Then, for each battery, we have to supply more than 100 solar power. I personally find optimal the number between 120 and 150, means 60 to 75 solar panels per battery. But in my setups constant drain never exceeds 1/3 of estimated maximum drain. You might want to calculate your own optimal.

By the way, one battery equals 50 solar panels power wise, while been 4 times lighter and 30 times cheaper.

Afterword: my personal thoughts

Honestly, for censorship purpose, I can’t wright what I truly think about this situation. But putting it most appropriate form:
Current battery power system is non-intuitive, illogical, irrational and counterproductive. Normally, anyone would expect power drain to split between batteries evenly.

It that case, solar ship with 460 solar power, 6 batteries and 2 small shields would be perfectly functional. 320 power constantly drains for shields, life support and other devices and 140 power goes into batts, 23 per tact per battery.

In practice, this setup would not work for the reasons stated above. Player have to change solar/battery ratio to 660 solar + 4 batts or 600 solar + 5 batts (making it heavier and more expensive) or jump throw other kind of hoops to make this ship fly reliably.

Seriously, battery system so broken, that I consider that as a bug. Hope, one day devs will fix it.

[Mojack]

The more people running test and numbers, the better.
Thanks for sharing your findings, Fifth Wheel.
Interesting, that power demand is going in serial order.
Batteries do behave wierd. On my setup, they still behave like I stated, but the percentage
seems to be way higher now, until the next batt will charge. I would need to run new test to
tell the new number, and test, if it has to to with the charge rate. (first observation was 8,8%)
Seeing is believing, so I would love to showcase that in a Video; but I cant at the moment.
However, in a few months I plan to do so.