solve this charging problem please

[HDIkyle]

Battery in boot using 25mm2 230amp welding wire. When running the battery getting around 13.5 to 13.8 tops but this drops to 12.5 to 12.3 with everything on (lights, amps, flowers and rad fans) at the front its its also giving out 13.5-13.8. This is since I have changed the earth from gearbox to chassis to the vacuum pump instead of the gearbox. Before this it was showing 14.2 at the front but only 12.9-13 at the battery.

Now its showing equal volts all round but only at 13.5ish instead of 14 as before is this likely to be an alternator issue? Starting to annoy me now as I don't know what then issue could be. Brand new silver Bosch s5 battery also

[Niall]

At what state was the car when you checked it the second time? Cold engine? Generally they won't charge at 14.4v until the battery is fully charged and there isn't any huge draw from anything.

[HDIkyle]

No engines hot been running a long time. But battery was flat as a fart to start with had it on charger before starting. How come surely it would give 14 out all the time?

[Niall]

That's why then.
No, 306s don't have smart charge so they will only put out a certain voltage regardless of load so more load, more draw, less voltage. The system is designed to settle at 14.4 when the battery is charged and under general use.
If it's an issue for you, you could fit a alternator from a mondeo of the same age or jag x type which have smart charge all built into the alternator.

[daddyfixit]

voltage drop through a long cable is normal, excess drop is caused by internal resistance in the cable being used.
check earth points are clean by cleaning with emery paper, also how are terminals attached to the cable at either end ?? crimping may not be enough---soldering is used as well on some manufacturers oe cables.

[HDIkyle]

They are soldered afaik it was a kit I bought of someone on the forums. Will charge battery tomorrow and try it then. thanks for the info