Batteries not charging

For preventive purposes I replaced my 4 year old AGM Moto Batt with an identical one. The bike wouldn’t keep the new one charged and I got stuck and had to be rescued by a friend. I believe I hooked the new one up properly but I did have to retighten the positive after I had the ground installed. I charged it up overnight with my battery tender and went on a 100 mile plus ride yesterday. The voltage just kept dropping.
I put the old battery in that I know is good and put on the trickle charger first- this morning. It started up at 12.2V but when starting voltage went down to about 8 before coming back up to settle at 11.9 (always says in the 12’s or above like 13.2) I went for a short ride- a few miles and it went down to 11.8- wasn’t showing signs of going up.
I put the volt meter on it at home and it showed 12.5 with the bike off and 12.2 on the dash when shut off. When I started it again, it went to 11.8V
I put the red lead from the multimeter on the ground and it read 0. I had read on another thread that’s how to check the ground??
Bike has been great until I changed the battery. Yikes.....
I’m not an electrical or mechanical wizzard. I’m just a student here. Thanks for your help.

John

Put my multimeter on the battery terminals and ran up the rpms. No change in voltage. I checked the ground at the starter- all good. Getting worried...

Others here will be able to advise you on your specific issue better than I can, but on the subject, I always carry one of these portable battery jumpers, just in case. Cheap peace of mind.

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Was advised to take one of the battery cables off while the bike is running as an indication that the alternator is bad. I took off the ground and the bike died.

Thanks for your advice Street (Pete).

Ok, I feel stupid but maybe someone else can learn something too. Was a blown 30 Amp fuse.

Im sure you just blew the fuse by shorting a wire to chassis and didn't notice
For future reference if disconnecting the battery always disconnect the Negative first.
When re-connecting a battery always re connect the negative last.
If you stick to that procedure you cannot short to ground.

Kiwi_Roy wrote:

Im sure you just blew the fuse by shorting a wire to chassis and didn't notice
For future reference if disconnecting the battery always disconnect the Negative first.
When re-connscting a battery always re connect the negative last.
If you stick to that procedure you cannot short to ground.

Good advise Roy, but I think getting this wrong would not blow the 30A fuse. It's gotta be something (perhaps momentarily) downstream of the fuse.

You are right Dave but any time you have the ground disconnected its next to impossible to blow a fuse whatever you short to ground there's nowhere for it to go.
It was quite common for owners of the spine framed guzzis for an owner to be unbolting the positive with a wrench and short it to the ECU letting out some magic smoke.
Our GRiSO are a bit more forgiving but it's still possible.

Pretty sure Roy is 100%. Correct.
Thank you both for responding.