bots won't use arc welder and will throw batteries out of it, but will use metallic foam sprayer just fine.
How to recreate:
1) give bot only arc welder
2) damage hull
bot will drop arc welder/its battery and refuse to elaborate

3) give bot metallic foam sprayer
4) damage hull
5) bot repairs it

seems like when bot tries to use arc welder he drops it or its items.

another thing i discovered, that when you add tag weldingfuel to a battery in sub editor arc welder works just fine.

maybe add something like high voltage battery for arc welders, that can be recharged where other batteries can be recharged. or reinforced battery with titanium/titanium alloy.

Someone mentioned the bots in the comments.
I unfortunately have no clue how bots work and don't have the time to dive into em.
Interesting workaround though, I'll see about just adding that as a battery variant for solo gamers out there.

i think best varient is reinforced batteries. and its usefull for small groups, where bots are keeping big sub alive

Don't really want to give em stronger battery than the original. Arc welders already destroy a lot of game balance by just existing. Honestly never played with bots, when we're gaming with a small group we just dive in a small submarine.

how about making those batteries worse than vanilla? this will make arc welders a logistic nightmare, but worth it.
Oh and you can make every electric ek utility item require it, instead of vanilla batteries. electric drill, jet scooter, rebreather etc

I just had a good idea on how to make that thing with batteries. So basically you add new item:

Name: High voltage battery cell

Description: battery cell, reinforced to work with high voltage. Can be used like normal battery cell, but very inefficient.

Crafting recipe: vanilla batery cell + titanium x2 + zink + fpga circuit

Tags: Batterycell (so can be put in vanilla things and bots will recharge it), weldingfuel (for arc welder), ek_hvbatterycell (to make requirements for advanced tools)

Main idea: ek tools can only use hvbattery, make hvbattery 50 charge (vanilla i think 100) so you can make hv tools consume less charge. So basically in vanilla tools battery will drain faster, than in hv tools

Too inconvenient. Can just increase the battery drain of the tools in the file if really needed.