Hilux Battery Sensor Issue

Had similar troubles with my old Renault Megane! Weak starts drove me nuts. Have you checked the voltage when the engine is running? It should be around 14V. If it's way off, your battery sensor might be toast.

Where exactly is the voltage sensor located and is it easy to check it myself?

On my Renault, it was attached to the battery. Easy to spot. If you don't find it there it may be near the alternator - I would advise going to a workshop, they should be able to help you.

Thanks. Took it to a shop and you were right, it was the battery sensor. Cost 315€ to replace. All good now.