Convince yourself to just use a 12V-to-AC-line inverter for LED light strings instead of rewiring them for 12V.

Step 3 Is it really worth it?

I also happen to have a 12V inverter to convert to line-current. Will that really waste the battery more than this?

Remember the sequences?:

Sequence  Voltage  For 12V  Resistor
G-B-R     11.4V    0.6V     20 ohms
O-Y-G-B   10.2V    1.8V     60 ohms
R-O-Y     9.2V     2.8V     93 ohms

Consider this spin: each of the 18 sequences of LED's will use 30mA of current for a total of 540mA or 0.54 amps. Note also that in the first sequence, 11.4V goes to light and 0.6V to waste heat out the resistor. Again at 30mA, that's 0.342 watts and 0.018 watts, respectively. If you do the math for the whole string, it's 5.54 watts of light and 0.936 watts of heat for an efficiency of 5.54 / (5.54+0.936) = 86%. That's in the ballpark of a cheap inverter.

So I connected up the inverter and found it drew 0.380mA at 12.34 volts which is 4.69 watts. Now the string is actually rated at 0.046 amps at 120 volts or 5.52 watts, wired without any large limiting resistors as best I could see (and it's very close to 30mA I calculated above). Anyway, this makes the actual efficiency of the inverter ( 4.69 watts / 5.52 watts ) = 85%.

I guess I could gain 1 whole percentage point of efficiency by going with wiring it by hand. In the end, though, it's probably not worth it.