89 civic Battery draining but new alternator
 

I have an 89 civic ran great no issues. The alternator went out but before it did it fried the battery. Put new alternator in and grabbed one out of my Toyota and it fried it. So bought a new battery Put it in started right up. We Went out the next morning battery dead. Runs fine all around town with a jump even at night with headlights on. I'm at a loss? What could be draining and ruining batterys like this??? Any help would be great. Thanks in advance.

Test that the alternator is working by measuring voltage at the battery with the engine running and everything else off. Should be about 14 volts. Trying to R&R alternator without disconnecting the battery first is likely to blow the 80 amp alternator fuse in the box next to the battery, which will prevent charging.

The next test is to diconnect the battery when you park so nothing in the car can drain it. If it is still live when you reconnect it in the morning to restart, common reasons for the car to drain the battery are the brake lights stuck on, light in the trunk stuck on, and aftermarket sound equipment.