agm battery voltage spike

[Goomz]

Hey guys, im having an issue (i think its an issue).  So my setup is a Singer 320a alternator, with an odyssey agm 24 under the hood, and i used to have a northstar smsagm80 in the rear.  I have gp car audio ofhc 1/0 solidly crimped for the big 4, and ran throughout the car from the main battery, to the secondary, and into a distro block into the amps. nut and bolt for ground on clean metal.   I say i used to have a northstar smsagm80 in the rear because i noticed it was swollen so i removed it.  (350a fuse for the batt+ to the alt, and 300a fuse ran to the rear batt.  from there, a fused distro block with the recommended fuse sizes that go into each amp accordingly. My subsonic is set to 29 hz, and my lpf is set to 90hz via smd cc1. gains are set via dd1+ with an 8db overlap on the mono amp. 3.5db overlap on the 4 channel. Pioneer head unit, 4v pre outs.

 

i have a crescendo sl1v2 and a crescendo s4 for my amps, and an smd vm1 connected to my ignition switch to read the voltage from the vehicle. The mono amp powers a 12" Fi ssdv2 in a gp box made for it tuned to 31hz.

 

my car runs 14.9v on the vm1 normally driving.  If i play music either rebassed or via apple music, if its a punchier bass note, like a kick, my vm1 shows a spike to over 15.6v.  I believe this is what caused my rear battery to swell up, but im not sure.  Is 15.6 safe for an agm battery dynamically? It cant be too good for the vehicle, correct? When the sub plays lower tones, voltage is fine. It doesnt drop under 13.8v and goes right back up to 14.9 on the vm1. Just wondering if its normal ( again, it doesnt sound good for the vehicles ecu and bcm to see spikes that high) or does that mean i need more battery reserve? Thanks

[All_Ears_On_Me]

Check your negative terminal on the battery and see if you have corrosion build up.

[revoracing247]

also i would connect the VM1 to different places and see what the voltage drop/spikes look like there. like at the battery, and at the amp terminals mainly.
15+ might not matter on the AGMs with short spikes (<0.5s). What it looks like is more that your electrical isn't up to par for your system. your transient current draw on kicks is too fast for your alternator to respond to (or stop responding to) and your battery capacity is too small to take the dependency off the alternator there.

Jumping to an LTO might be the easiest option here. Or adding enough AGM's to take the load off the alternator on transients and make the constant discharge/charge abuse off each battery individually too.

Just my 2 cents.