Stereo cuts out when stop/start operates, is it always due to voltage drop? thoughts on a fix, please.

[Leadfold]

I have an upgraded Sony stereo fitted to my T6 and it cuts out when the starter motor kicks in on stop/start. Western Car Radio told me it was due to voltage drop (and most of what I read seems to confirm this). They suggested a new battery, which given that in every other sense it is fine, was an expensive solution. So I opted for the in-line capacitor they offered to fit, as a means of holding the supply of power for the moment when the starter kicks in. Sadly this hasn't worked, and the stereo still cuts out on engine fire up. However, the radio does now stay (for about 10 seconds) on when the ignition is off and the keys removed. Which seems odd to me. If there is enough power in the capacitor to keep the radio on for 10 seconds with the battery disconnected, why cannot keep it on whilst the engine restarts?

So my questions are:

Is this issue just down to voltage drop, or could it be something else?

Will a new battery definitely fix the problem? (I recently fully charged the vehicle battery and if I am understanding it correctly the Vitron charger is telling that the battery is holding 34Ah).

I will be fitting leisure electrics in the coming months (Li-on battery etc). Can the stereo be wired to this?

Any other solutions?

Your thoughts welcomed.

 

[Howzat]

I had the same issue when fitting an external amp to the headunit.
Fitted a Bosch S5A13 starter battery which greatly reduced the occurrence of it and even when it does happen it's less noticeable.
Wiring to the leisure battery would introduce a whole host of other issues because you'll be bypassing the BCM control.