I don't wait till my car is stuck in the dead of winter with a dead
battery to replace it. I have 4 daughters that drive, so you can
understand my concerns. I usually have a couple of car batteries
kicking around here. I'm actually getting ready to go off the grid
with my R75 and 2m rigs as well. My 2m rig actually displays the
battery voltage for a few seconds when power up.

I don't think I need to be worried about creating hydrogen from
charging a battery in the basement. Do I? It will only be a trickle
charge.

So there ya go. Go look at your loved one's car battery and if it
looks like it might be a little iffy why just yank it out and drag it
into the shack. Tell the old lady your concerned that she might get
stuck this winter and have her fork over the cash for a new battery.
Everybody is happy.

73
Bob