Be REAL careful with the old UPS guts. Lots of them are designed to be operated completely enclosed in either an internally insulated, and externally grounded metal case, or in a screwed-together insulated plastic box, so nothing in their circuitry is fully mains insulated, and EVERYTHING - even the battery - may be hot with respect to mains ground. Touch almost anything, even the 'insulated' heat sinks, and you may receive an AC shock.
Check for AC volts to ground on the battery and the obvious 'exposed metal' of heatsinks etc before you run it uncovered, or before 'der dumbkopf mit der gefingerpoken' begins playing around.
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