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Charging voltage increase hilux gun125
Hilux GUN125 2.4d 2016 model charging voltage is 13.7-13.9v
The car has an 80ah AGM battery that requires a 14.7v charging voltage to stay full.
In Finland, we have to warm up the car's engine in the winter before starting it. the car has a diesel-powered additional heater.
this heater requires a lot of power when it starts.
I have a toyota scanner with which I can raise the charge when the device is connected, but it cannot remain high when the device is disconnected. I have to charge the battery in the winter every week to keep its charge high enough. have you managed to raise the charging voltage of the car charger in some way?

This issue has been mentioned before , but there is no way of increasing the output of the alternator it is fixed at 13.9v. The very early models were fixed at only 13.6 !!.

All you can do is use a 40amp DC/DC converter to charge an auxiliary battery and then use the aux battery for starting the engine.

Why did you change the orgininal battery whats the advantage of the agm battery which is going to cost you another alternator to charge it properly. I don't understand what you think you are going to achieve?
Put the orginal type battery in it keep it simple .

Even the original battery didn't work without charging it. the car should charge more than 14.00v for any battery to work in it.
I had an assumption that the charging voltage can be increased as in older models. With the Toyota scanner, it can be raised to 14.8v, but it cannot be left on. I think the ecu adjusts the charging voltage. I'm trying to find out from the programmer if he can set it higher. This issue applies to all brands of cars
is a fuel-powered engine heater. The battery must be charged in the winter so that there is enough power for the heater. The problem is only accentuated in this newer Toyota Hilux model, which has a poor charging.

I think what 241Steve & Numberplate were trying to say (please correct me if I'm wrong) is that your best solution is going to be to setup an Auxiliary Battery that is used for your heater only and it is then charged from a DC-DC charger from the existing alternator that will also charge an appropriate Engine Start Battery. If you choose a bigger auxiliary battery system then you might also choose to run other loads from this system ... Camp Lights, Compressor, Whatever your desire might be.
13.8V is the nominal charge voltage for automotive systems. Trying to increase this runs the risk of burning out other components within the vehicle. Start burning things out and you risk fire and the chances are that no insurance company will want to know you if they find out what you're doing.