Battery charge lossiness issues
Space Engineers version 01.100.024
Based on my own testing, I believe that batteries are NOT 100% efficient when charging under any circumstances, not even when charging from Solar Panels.
I made a largeblock ship in Creative, put 100 Solar Panels (total output 12 MW, what the battery claims to accept), a Cockpit, and a Gyroscope on it, pointed it right at the Sun (using a non-rotating Sun), then removed the Gyroscope and put a Battery on it. I then switched the game to Survival mode, waited to make sure the Solar Panels were generating 120 kW each (so about 10-20 seconds), then set the battery to Recharge On.
The initial time estimate said that it would take 15 minutes to recharge. I clocked it with a stopwatch at 19 minutes, 40.83 seconds. That's 3 Megawatt-hours in 1181 seconds (rounded off). 3 MWh = 10800 Megajoules. 10800 MJ / 1181 s = 9.1448 MW, or about 76.2% of 12 MW.
So, not only are batteries lossy when charging from any source, the "Fully recharged in" time estimate is lying to us.
I also noticed in other testing that batteries are lossy when charging from other batters, so I think that this lossiness is on any battery charging regardless of where the energy is coming from.
I'm updating the wiki article accordingly.