I would say engine. The smallgrid battery has 200kw max output, according to the documentation (haven't tried any oil related stuff yet because I haven't found any oil), the output on engines is 1,5 MW on SG. That is 7 batteries and you also save a lot on weight there.

Rümmler.363VD ✠ の投稿を引用：

I would say engine. The smallgrid battery has 200kw max output, according to the documentation (haven't tried any oil related stuff yet because I haven't found any oil), the output on engines is 1,5 MW on SG. That is 7 batteries and you also save a lot on weight there.

You are talking about SMALL SG battery.
A SG battery have 4MW 3x2x3 1044kg, a fuel engine have 1,5MW 3x2x2 966kg.
So my question is about fuel/space/weight.
If battery have better energy density, output and weight, fuel engine is useless

Oopsie, guess I made a mistake right there.

In vanilla, h2 engines are meant to be as backup power; since gasoline engines are tier 2 h2 engines, it makes sense they still are backup power.

Some of my (vanilla) blueprints have backup engines. It can be useful sometimes.

Rovers can actually run pretty well on h2 engines + storage. Using the gasoline engine makes it even more efficient.

Using lithium batteries requires a higher tech tier and is more efficient, but getting the fuels can be quite early in a game.

Rümmler.363VD ✠ の投稿を引用：

Oopsie, guess I made a mistake right there.

In vanilla, h2 engines are meant to be as backup power; since gasoline engines are tier 2 h2 engines, it makes sense they still are backup power.

Some of my (vanilla) blueprints have backup engines. It can be useful sometimes.

Rovers can actually run pretty well on h2 engines + storage. Using the gasoline engine makes it even more efficient.

Using lithium batteries requires a higher tech tier and is more efficient, but getting the fuels can be quite early in a game.

I built a big SG lithium battery from small SG cargo drops batteries, i was thinking "as IRL gasoline will have a lot more energy density than lithium and to be a lot more abundant, or gasoline will be a very big waste of time".
I found lithium ore before crude oil.
So should i invest in gasoline for energy density or solve everything with lithium?

I did the same as you, skipping oil entirely because it is super rare / hard to find. Well, I dropped on earth 10m next to a lithium deposit, could have been pure luck.

While browsing for niter I got annoyed and went creative just to see if it even spawns. I found 1 oil deposit and 1 niter deposit on earth. Seems to be rare. I am using deeper ores module.

Farming the Lithium cells for the first LG battery was a bit tedious but made the progression much more fluent afterwards.

I don't know if gasoline is helping you with electricity that much, however there is rocket fuel made from Oil and afaik it's tier 2 after hydrogen. Not that I need that much thrust for my first space trip anyway. However, crafting polymers from sulfur and carbon takes ages and you need a lot (and I mean REALLY alot) rubber for the last tier tech blocks. A jumpdrive takes a whopping 6000 rubber. My guess is that refining oil and grabbing polymers doing so (instead of going the synthetical route) saves time on that. I haven't tried any oil though.

Gas is great for long duration power production. Small grid engine plus a 3x3x1 tank will give you the 1.5MW for almost 2 hours. So complement the batteries well with gas providing the energy and batteries meeting the peak load needs. Plus the Acid battery produces barely more power at 2MW and only for 15 minutes.