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I've looked into it a bit as I'm in a similar scenario, council garage/lockup with no power or water.
The thing with the portable power stations other than the £500 price, it seems that once you calculate mAH, you actually don't get many minutes of power tool time before it needs charging. Unless I'm doing my calcs wrong and someone wants to correct me. So it probably makes more sense (although I think it's more money) to invest in battery powered tools rather than corded, and individually battery powered LED lights.
If you've already got the corded tools, it's not ideal.
My current idea is to invest in a portable power station, then I can run led lights with it and the added benefit of being able to use other appliances/tools. For my usage I can't see having to charge it that often.