Today I installed a new battery on a 1980 Ford F250 V8.  Just tested the battery when engine is running, volt meter shows 12.25.  I guess that means my alternator is bad.

The truck will sit until next Wednesday when I have a scheduled front end repair at a local shop.   Will the battery last until Thursday if the only driving I do is 4 miles to the repair shop Wednesday and then one more drive of 3 miles the next day to a shop to get a new alternator?

if you unhook the battery neg till you need it, you should be fine.

if you have no aftermarket accessories, you might be ok leaving it hooked up. but if it were me, I would pull the cable and put it back on before each drive.

Andrew, no aftermarket stuff.  Thanks

What will unhooking the battery do when he's not using the truck?

he is talking about driving it a total of 7 miles.

in a 1980's truck. So it might be electronic ignition and carbed, since efi wasn't standard till around 89 ish.

the starter would be the biggest draw.

keeping the blower motor off for heat and lights off 10 miles should not even be a sweat for a new battery.

disconnecting it prevents parasitic draws from draining the battery while sitting for x number of days.
more critical for newer cars but if he had something aftermarket on it, that could down it fast too.

radio's pull power to maintain radio station presets, alarms keep the alarm radio active so you can arm and disarm with the key fob, etc..