Hi Peter I note your replacement of the sealed batteries in the UPS with old
car batteries. The UPS will charge them correctly but the car batteries will
produce hydrogen, I believe, even on a maintenance charge. The sealed
batteries are designed not to produce hydrogen (by careful design of the
electrode sizes) unless maltreated ( then they bulge alarmingly ). I know
your shack is in an extension and hope it is well ventilated.

A Radio Club member at MRS was involved in a nasty accident with
professional battery back up rack, when a techician walking across a carpet
to test a battery (backing a professional link circuit) drew a static spark
as he reached for the vent caps and and was drenched in battery acid, by the
resultant explosion. The amateur present was able to sluice him with water
immediately, and use eye wash bottle. He suffered no lasting effects other
than the need for a new pair of shoes and trousers, and an healthy caution
when approaching lead-acid batteries.  If the batteries can be located
outside in a ventilated cover box it would be safer, particularly with the
voltages and possibility of sparks involved in LF transmitters. At least do
keep an eye wash bottle nearby. It is better to be safe........

Cheers de Alan G3NYK
[email protected]