Hi,
I have a solution, already tested in another project, without relay that is very much reliable, is totally disconnected from the "high power" cables of the battery and is upgradaeable as well.
I can provide the schema to build such device that can be managed/controlled by a digital input, the MCU will not blow up because of the relay because there's no relay. Of course it can blow up for other reasons that have, eventually, to be investigated.
Please confirm that you already have the code written and no coding is required, the bid covers only the schema of the device that replaces the relay, no debugging of your code, no fixing of anything else.
Cheers,
Alex.