Inline battery tell me how?

[DAVE FERENCZ]

My truck has hard warm start. Had both batteries tested- replaced one. I have read that inline batteries give more power for warm start. I would like to try this before doing the fsd thing. Please advise me on this.

[gmctd]

You did not mention year-model, but late trucks are computer-managed systems, powered by +12v batteries, paralleled for cranking power.
Series batteries would be +24v, at which level your vehicle would become computer mis-managed and dis-functional (read: dead).

Believe it or not, batteries should be replaced in pairs - if one is dead or dying, the other is not far behind.

Battery cables and connections deteriorate in oxygen - oxidation and corrosion limit cranking power.
Check all connections at battery, starter motor, and engine ground.
Check cables for hidden corrosion.

Starter motor bushings, bearings, brushes, and built-in solenoid switch deteriorate over time, resulting in 'dragging' starter.
Draws more power than necessary but turns over slower.

Give your truck a good winter going over - it should return to easier starts, cold or hot.